I'm new around here and therefore a little hesitant to comment. But I do have a point of view that I don't think has been mentioned. First, I'll say that my handful of experiences at MAC stores and counters have been great and I've never returned anything.
That said, about 2 years ago, I went to a Chanel event where I got a full facial and makeup application. I had paid something like $35 to attend the event but was under no obligation to buy anything. The MA applied a foundation and dickered with it (I mean they put lipstick on my face to "cut" the redness) until it was the right skin tone and then went on and on about how I had to to have it, drawing in other artists to confirm. I had never purchased foundation before and was totally green about what he was doing. Needless to say, with all of these professionals cooing at me about how great I looked, I bought the foundation (and a few other products).
Long story short, I wore the foundation a couple of times and then saw a photo of myself where I looked like a crazy, painted kabuki actor. I promptly went to MAC, had an artist find me the right shade -- NW43 -- and have not looked back. I have no idea what Chanel's return policy is because I never returned the foundation. But I know I will never approach a Chanel artist or buy anything other than skincare from them them again.
Obviously, there are people who abuse the return policy but for me, knowing that I can return something that I end up hating in the cold, hard light of day keeps me loyal to the company that offers that kind of insurance.
(On the separate but related note about returning things other than cosmetics, I do this all the time. If I go to the store and the dressing room line is a mile-long, I'll buy it, try it on at home, and return it if it doesn't fit. Or I'll buy to match something else in my wardrobe and return it if it doesn't work. If I haven't worn it, the store can re-sell it, and the salesperson isn't losing commission on it, I can't see why a cashier would consider me "entitled" or annoying.)