Google Shopping isn’t an online marketplace and doesn’t directly sell any products, so it can’t really be compared with other eCommerce stores. To put it simply, you’ll never purchase a product directly through Google Shopping. Instead, Google Shopping compiles products from various online shops and retailers and then promotes those. When a user performs a search, it shows all the products relevant to the user’s query.
If a user decides to click on one of the featured products or Google Shopping Ads, they’ll be taken to the relevant online shop. That is where the final purchase and transaction will take place.