Wanted to try a different size in the best bra I've found so far. One clerk bombed out on me. (Why do some of them march down the center isle without looking to left or right, which is where the customers are.) Told them I found the size but didn't want another black bra. One young clerk with glasses went into the back room and found 1 beige, one white. Then did I get a surprise!
Tried on the black and the beige: they didn't work as well as the size I had at home.
Then I tried on the same bra, same size, in white! It was completely different and gives me a great, becoming fit! In this case, the fact that the manufacturer could have had more quality control was good for me.
Meanwhile the clerk who actually helped me disappeared, but I stayed around until she came back. I wanted her to have the sale, because it's rare to get someone who really helps.
Moral: from now on I try on several even though they look alike.