Yes, it's available only for e-commerces in The U.S. There are currently Amazon, eBay, and BestBuy but it doesn't stop someone out of the USA to use the website if the person is looking to buy BTC without KYC (out of the traditional methods).
If you're considered a 'Shopper' reputed you can get a nice discount on your orders
If you're 'Earner', there are limitations contrary to what the OP says, although it is still quite high
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It's a similar system to Purse.io with the same downsides.
1- Unfair discount system based on the user's reputation. Because some users give negative feedbacks for no particular reason. On Purse.io I had received 1 negative feedback because the person had received his package 24 hours late (or something like that) LOL
2-There is always the possibility that the person is using a fraudulently obtained Amazon gift card and you could be the one in trouble afterwards. Not to mention those who cancel the Amazon order.
Both are good websites but sadly we live in a fucked world with people always trying to abuse systems :/