Google Search results differ from user to user. That includes products, to some extent.
So how does Google decide which organic product listings to show users? Well, it depends but it all goes back to data—data merchants provide, as well as personalization data.
Before we dig into how Google decides which product listings to display, let’s quickly review Google's main product marketing programs:
Surfaces Across Google is an unpaid Merchant Center program that allows your products to be seen by customers, at no cost to you.
Google's most recent change to the program puts it front and center as it's now responsible for all non-paid listings across all of Google Shopping.
By opting in, Google adds your products to the Google Search Index. In return, participating merchants become eligible to appear on surfaces across Google (Search, Images, Shopping & Gmail). On one hand, all businesses can (and should) take advantage of the opportunity – which means lots of competition. On the other... it's hard to argue with free.
If you sell products online, you don't want to miss out on free Google exposure.
Originally commission-based, Google has transitioned Shopping Actions into a free program.
Google Shopping Actions enables merchants to list their products for sale on Google. Not to be confused with Surfaces Across Google and the general surface that is Google Shopping. Participating listings are actually sold on Google – they're marked with the "Buy on Google" badge.

Shopping Actions products are only pushed on traditional Shopping surfaces when Google can nearly confirm that a product would be a perfect match. However, you can always easily search through “Buy on Google” options exclusively, or browse Stores on Google Shopping to find a wide array of GSA products.
Additionally, products sold on Google are available to order through Google Assistant and should soon be available through YouTube, as well.
If a user is logged in, Search results and Images Search results are personalized – along with a lot of the rest of the Google experience.
On Google Shopping, however, results don't change much from person to person. Similarly, the results displayed for a "Buy on Google" filtered query would be the same for all searchers. The higher a product is here, the more optimized its data.
Products with good visibility in Google Shopping are going to fare well as organic recommendations if and when ideal searchers come looking for it.
When Google first evaluates your ads, the only thing they’ll be reviewing is the product data you’ve provided.
While this is basic information, it’s a step that can’t be overlooked. Google doesn’t want to risk making assumptions about your products when it comes to ads. If you aren’t including the most basic information, they won’t appear in Search.
The product attributes Google requires for products are fairly straightforward. Here are the most important attributes that you must provide to Google:
Build out your data as much as possible. Your listings won’t run without all required attributes, they’ll run better with all possible attributes, and they’ll run best if all of those are optimal.
The more good product information you provide, the more likely your products will be shown to your ideal audience.
Run a free feed audit and see which of your titles are matching queries you'd never choose to bid on.