Analyzing their own sales and analyzing other people's sales on their platform are two different things. Saying that Walmart may also try to do this in the future does not make it right or excusable.

How is it different? The same outcomes and potential power abuse happens in both situations.

Who takes the risk in each scenario is different. If Amazon was only using their own sales data then they'd need to start selling a more diverse range of products themselves to acquire that data. Some of those products would sell well and some would be flops. Amazon would have invested money into selling all of them so the cost for the flops negatively affects their bottom line.

In the current scenario someone else sells things on Amazon and is taking the risk that the item they're selling will not sell well. If the item is a hit, Amazon swoops in and starts selling it themselves or possibly makes a competitor and sells it themselves. Either way, Amazon reduces their own risk of selling poorly performing products while also cutting into the upside for the vendor who took that risk when they are successful.

Edit: I forgot to mention above that the people taking this risk are paying Amazon to do so.

I really think you don't get the point of how Amazon marketplace works

> Just because they purchase and resell inventory doesn't mean Costco (or Walmart or Sams Club etc) doesn't hold the same power over their product suppliers that Amazon does

With the Costco example, Costco as a retailer holds power over their product suppliers. If they are making an own brand, what they are doing is buying it from another supplier and asking that manufacturer to put their own label on it. These relationships can be anti-competitive and present opportunities for market-abuse, but in a meaningfully different way to the Amazon example.

With the Amazon example, Amazon holds power over other retailers using their platform.

And with the Walmart example you have stated, I do think that suffers from the same problems.