This right here is why I never believed the claims either.

I get the claim of they buy the key in lesser off regions for cheaper to sell at a higher price but, steam dashboard allows you to individually disable keys for any reason you like. I wouldn't imagine anyone actually daring to try to resell those(review keys), they would be blacklisting themselves from the industry.

There's the argument that the publisher/dev might be new to it and didn't log who got what key but, I wouldn't bet access to games on that.