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Amazon blocks non-Prime members from buying certain video games(r/Games)
So, if you check the listings for GTA5, you’ll see that the Amazon listing is ~$5 cheaper than the rest, and only for Prime members. Of course, you can still choose to buy from one of the other sellers at the normal price.
So unless I’m missing something, Amazon is just giving better deals to their Prime members and leaving the rest of the sales to third party sellers. It sounds more like a poorly communicated sale than some attempt to prevent non-Prime members from buying games.