As long as it's policy, do WHATEVER you want.
I do refuse to believe that "luck" has anything to do with people that return 6 (or more) of the same product though, ESPECIALLY when they claim they have "seen" that elusive perfect model before. I am certain that with enough scrutiny they would definitely find a "flaw" with the "perfect" one too, they just need that image in their mind to strive for to justify the lunacy.
If you don't like the QC: DON'T BUY ONE. I am so tired of people acting like they have a gun to their head forcing them to buy/use Apple products, and how they "deserve" a "perfect" (screen, coating, shell, everything... etc.) because they spent money on it.
Again, it's perfectly ok to wreck a nice store policy. It's your right as a consumer. It's just ridiculous.
If you need to open more than 2, you are likely to NEVER be satisfied, and may as well look elsewhere. It's really ok. No one is telling you that you have to be happy, just that it's silly to open box after box looking for a unicorn that doesn't exist (at least to your standards). And cut the "my standards aren't that high"... they are, and Apple isn't meeting them. Time to move on.
It's really ok.