Why Use Google Comparison Shopping Services? An Introductory Guide

Google Shopping is one of the most powerful routes to reach high-intent shoppers - people already searching for products like yours. But what many retailers don’t realise is that you can’t advertise on Google Shopping directly. You have to do it through a Comparison Shopping Service (CSS).

Working with the right CSS partner can transform your visibility, efficiency and sales - helping you reach more customers without increasing your ad spend. But how can retailers make the most of Google CSS? Keep reading to find out more.

Our introductory guide to Google CSS will help you cut through the complexity by explaining clearly how Google Shopping Ads work, what a Comparison Shopping Service actually is, and how working with a CSS can help you reach more people and increase incremental sales without impacting your current advertising costs.

What are Shopping Ads on Google?

When you search for a product online, adverts from Google Shopping will be prominently displayed on the results page. The most common examples are Product Listing Ads (PLAs), which are typically displayed above the organic search results in a carousel format.

Google’s product comparison service originally launched as Froogle in 2002 offering free listings for merchants. Since then it has grown massively in importance and prominence to businesses, customers, and Google itself. 

The effectiveness of PLAs led to the introduction of a paid auction system for advertisers, and the available space increasing to up to 30 listings in one carousel. Shopping ads were originally triggered by very specific product search terms, but they are now activated by more generic keywords and phrases.

All Google Shopping advertising is controlled at a product level, requiring a data feed to be created and uploaded to Google Merchant Center for Shopping Ad campaigns to be created.

It’s a form of advertising which has been embraced by both retailers and consumers. In 2018, around 80% of all paid search spending by retailers went to Google Shopping, and it received around 88% of all paid advertising clicks from customers. 

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What are Google Comparison Shopping Services (CSS)?

A Comparison Shopping Service (CSS) is a Google-approved platform that lists your products and runs Shopping ads on your behalf. Every retailer advertising in the Google Shopping carousel does so via a CSS - including Google Shopping EU itself.

However, there’s a big difference between using Google’s own CSS and partnering with an external one like Redbrain.

Google Shopping EU automatically adds around 20% markup to your bids to cover its profit margin.
By working with a Premium CSS Partner, that 20% is removed — instantly improving your bidding power and increasing your visibility without costing more.

It’s one of the simplest ways to improve your Google Shopping performance.

Why do retailers choose to work with CSS partners?

Partnering with a CSS unlocks more visibility and efficiency in Google Shopping. Retailers benefit from:

• More reach for the same spend — without Google’s built-in surcharge
• Access to advanced AI bidding and optimisation tools
• Performance-based models (only pay when you make a sale)
• Better feed management and data enhancement
• Expert insights and ongoing optimisation from dedicated teams

In short, a good CSS partner helps you win more impressions, clicks and conversions, not just manage your listings. Research by affiliate network, Awin, found that CSS as a channel has seen growth, even as other channels struggle, with CSS applauded for its ability to acquire new customers.

How do Google Shopping ads work?

When someone searches for a product, Google runs an auction to determine which listings appear in the carousel.
Your CSS partner enters that auction on your behalf, using your product feed data from Google Merchant Center.

Your ad placement depends on:

• Your bid
• Product relevance and quality
• Data accuracy and feed optimisation

Because CSS bidding is auction-based, your costs can’t be artificially inflated. You’ll only ever pay the next highest bid amount. The better your feed and relevance score, the more efficiently you’ll perform.

Who can be a CSS Partner?

Every CSS has to meet minimum requirements to operate with Google Shopping, so your existing PPC or marketing agency is unlikely to qualify - but they can work with any CSS on your behalf.

To help in choosing the right provider, Google has introduced a CSS Partner and Premium CSS Partner program. This lists services who have been officially certified for their skills, training, and experience. In return for meeting the requirements, Premium CSS Partners such as Redbrain gain access to higher levels of support and training from Google, and are likely to get earlier access to new opportunities.

Since 2017, Google Shopping EU is listed as just one of the Premium CSS Partners you can choose by country, industry and supported language.

Fortunately, the decision of picking a CSS has been made easier by the design of the Shopping Ads auctions, which allow you to use multiple partners at the same time, without increasing your costs. In fact for most large retailers it can be beneficial to work with multiple providers.

Choosing the right CSS partner

Not all CSSs work the same way. The right one depends on your business size, goals and structure. Here’s what to look for:

1. Service Models: A Managed Service will let you provide your product data directly to your CSS, and they handle optimising your feed, uploading it to Google, and managing your campaign. Self-Service means you manage your Merchant Centre and Google Ads accounts once they’ve been created by your CSS.
2. ‍Bidding Strategies: Each CSS will have their own approach to effective bidding. Some will focus on specific products rather than your whole inventory, or go through manually creating account structures and bidding optimisation. Whereas the Redbrain machine learning and AI approach works through the day and night to implement Smart Bidding on every product.
3. ‍Experience and expertise: This doesn’t just apply to implementing bidding. In addition to the quality controls and requirements enforced by Google, pan-European campaigns require a knowledge of the laws and product restrictions in each country.This comes largely from experience, working with thousands of retailers on a daily basis and providing solutions for every challenge they might encounter.
4. ‍Additional Services: Data enhancement and optimisation can deliver a big increase in sales conversions. And the wealth of data from a Premium CSS Partner can feed into your other marketing efforts, along with providing answers to any queries or problems which may occur.
5. ‍Billing Models: Many CSS providers will operate on a Cost-Per-Click (CPC) basis with an additional fee on your bids or a monthly retainer. For example, Google Shopping will add a 20% charge onto bids before they are entered into the advertising auction. But it’s possible for an optimised campaign to be run on a CPA basis, which means you only pay a commission when you make a sale.
6. ‍Technology:  If you stock thousands of products, it will take a huge amount of time and manpower to scale optimisation across your inventory. This means AI, machine learning and automation are essential, in combination with expert oversight and input, to promote everything you sell effectively.
7. ‍Reach: Experience and huge amounts of data come with scale, allowing your CSS to benchmark your efforts and understand where the biggest improvements can be made. Look for partners who have worked with high volumes in the industries and regions which apply to your business. One key comparison will be the size and reach of each CSS website. Does it reach millions of visitors who will also be directed to purchase your products?

Are there different ways to work with a CSS partner?

There can be lots of factors involved in choosing a CSS partner, which are explored in detail below. But one of the core differences will be the way you work with a provider.

The three main routes to advertising via Google Shopping Ads with a CSS are self-service, a managed service, or a hybrid of the two.

For example, Google themselves offer a self-service model, but can also offer consultancy. The majority of Redbrain customers benefit from a Managed Service, although self service is offered to specific clients if required.

With self-service, the CSS will create the required Merchant Centre and Google Ads accounts on your behalf, and leave you to manage your feeds and campaigns.

A managed service will let your CSS optimise your product data feed and manage your campaigns, whereas hybrid models can be a mixture of the two approaches.

The other major difference between CSS partners is how they will bill you for the work they carry out on your behalf.

How do I pay CSS partners?

Every CSS partner will bill for their services based on one of three models. Either they will invoice a fixed monthly retainer, Cost-Per-Click, , or some, including Redbrain, offer a Cost Per Action (CPA) service which charges based on completed sales. Essentially you only pay a commission when you’ve received a new customer.

Ultimately your choice of CSS partner should be based on more than just their billing model. But a CPA model does show confidence in the results a CSS believes they will deliver for you.

Can you work with multiple CSS partners?

For the vast majority of merchants it’s best to use multiple CSS partners and bidding strategies. This will enable you to reach the biggest possible audience, as the efforts of each provider will be complementary rather than antagonistic, so you get the best of the results from each service.

Providers may rely entirely on human expertise to choose key products to feature, create campaigns and manage bidding. This will operate differently to a service such as Redbrain, which adds skilled staff on top of a machine learning AI platform and Smart Bidding to scale our insight to a larger range of your product inventory.

It also opens up the opportunity to appear more than once on a single results page. Although two CSS services can’t both appear for the exact same product from one retailer, it’s possible that two different products might both qualify. Or you could appear in two Showcase Shopping ads because you’re working with both CSS partners.

How to be successful with Google CSS

There are two main areas which form the basis for success with Google CSS. The first is the quality of your business offering, and the second is your partner strategy.

Fortunately, the best practice for Comparison Shopping Services matches up closely with a good general eCommerce business plan. That means it will also improve your results in other areas of marketing, including other Google Shopping and Paid Search advertising, and organic Search Engine Optimisation.

The starting point will be to ensure your business meets all the requirements to advertise. And to assess the quality and performance of your website. A good indication of success with Google CSS is an effective existing conversion rate, as this shows increasing visitors will be likely to result in more sales.

Your inventory should be competitively priced. And the product information should be enhanced with good quality images and reviews from previous customers. Stock availability is also important, particularly as it can create issues with your data feed.

The other indication for success is that there is sufficient consumer demand for your products. This can be shown by the search volume for individual items, or the product category.

A successful partner strategy will depend largely on the size of your business. For bigger or strong niche brands, working with multiple CSS partners will deliver the best results.

If you’re a smaller brand with less inventory, then there may not be enough differentiation between providers, so it will be better to focus on working with one CSS. You’ll still benefit from making the most of the available search volumes, and be best placed to increase sales as your business grows or your industry niche expands. Choosing a Premium CSS Partner will ensure a higher level of customer service and experience due to the eligibility requirements Google has, so it will save you trialling multiple providers.

You have 4 levers to drive success with Google CSS.

• Your Offering: Quality website, products and data feed, with a good existing conversion rate
• Your Competitiveness: Products are priced well, with good reviews and availability
• The Market Demand: Customers are actively looking for products and there’s sufficient search volume.
• You CSS Strategy: Picking the right partners, brand and marketing strategy, and the right commission rates (for our managed CSS services)

Retailers who master these four levers consistently see higher ROI, improved efficiency and sustained growth.