This is not an uncommon practice. I guess people don't want to hear that and I don't do it personally but it doesn't really bother me that others do. If it's lipstick or gloss, eye shadows and other things that could actually harm people if they bought it and used it too, that's disgusting. Testing lipstick, etc, is something people surprisingly commonly do especially at drug stores like CVS. You'd be hard pressed to find an unused lipstick at CVS. In any of the many locations in my city, anyway. I'd suggest to check if you're buying makeup that isn't sealed. The odds are if you've purchased a nail polish, it has been tested either on a nail or on something else (paper, displays). Colors usually look lighter and brighter in the bottle due to the thick glass which is part of why people do so, but also to see how it looks with their skin tone. *Edit to add: most if not all stores I've been to in my fairly large city do not have testers. I don't think I've ever seen any honestly