I recently returned a studio fix compact, because I'd been color matched by two different MAs, one said I was an NW20, the other NC20. I went with the NW, since it didn't look bad in the store. But at home, it was wayyyy too pinkish for me. I had only used it the one time. The MA was perfectly nice about it, gave me a fresh NC20 and I haven't had a problem.
I know people do abuse the return policy, but in this case I was really, really grateful not to have to keep the wrong shade because of an error like that. I wouldn't have been able to afford paying for the correct color, and it's nice knowing that MAC really does want you to look your best and be happy with your purchase. I'd be sad if MAC changed it's policy just because a few jerks try to get something for nothing and ruin it for everyone.