'Test' Samples. lol. Nah, I don't really know. It depends on the item. I think if you return a matress, it has to go through the entire cleaning process again (And if there's any stains on the mattress, they won't let you return it).
Some items can't be returned once they are open as well, some places may not allow you to return something like mascara...
But otherwise, many places just state that it's used, and reduce the price... some people might buy it anyway.