And there are often many different listings for exactly the same product.

And sometimes there's one listing for similar products. I bought a Lodge cast iron skillet today. They've clubbed nine different sizes into one listing, there are over 8000 reviews and over 500 answered questions.

Q: "What's the actual size of the base?"
Ans: 8"
Ans: 9"
Ans: 3" ... WTF!

The reviews are similarly mixed for all eight sizes. Here the items are basically similar but if you were interested in buying a really large skillet wouldn't you want to read the reviews for just that size? Too bad, there's no way to filter it down. Sometimes there are different materials used for similar items, the other reviews are completely meaningless then.

IMO, for verified purchases, there shouldn't even be an option given to specify the exact product purchased and the seller. These fields should appear automatically for the review and the user should be able to rate and review both, product and seller on a comprehensive review page. I'm guessing Amazon has given these processes a lot more consideration than we're giving them credit for and the resulting system is one that hurts their sales the least.

I imagine that people check this for anything that's not Prime (I know I do).

I can't imagine most shoppers doing this. In any case, it's something I've learned the hard way to do in the future.