Foreign shopping websites have a hard time settling in Poland as we have a very strong local competition - Allegro.
eBay tried some years ago and failed miserably. It exists but I never thought of shopping there.
When Amazon entered Poland with a dedicated regional store, they had to introduce a very attractive offer to bring customers. Hence I pay an equivalent of about $13 per year and for that I get Prime Video, Prime Delivery and Prime Gaming. However I find Amazon store itself pretty lame. The app UI feels inconsistent and unintuitive, like someone took a different app and decided to build something else on top of it. Offers don’t have regular titles but instead there’s a waterfall of search keywords. Both titles and descriptions seem auto-translated from other languages. Prices are often higher or much higher than in other web stores. Basically a lot of them look scammy.
So to answer the question, I made a few purchases on Amazon but it’s not my go-to place. There’s a lot of online stores and there are websites that compare prices between them so in the end I will buy at a store that gives me the best bargain (good price, fast free delivery to a parcel locker, seller credibility).