Yet again Lemmy shows that much of the userbase is young and has little general knowledge. A/B testing is quite standard, and there is nothing shady about testing different prices to see what consumers will purchase more.
A couple of times I've been walking in a mall (dating this anecdote back a couple of decades or so. heh) and got asked to participate in product testing where I was shown - in the case I remember better - two cans of soda with different designs. Strawberry soda - one pink can, one red can - which one I was more likely to purchase.
A/B testing is quite common as companies figure out how to sell you more. Assuming it's randomized, it's completely ethical.