Envato’s refund policy states, in part, that a refund may be granted:
If an item doesn’t work the way it should and can’t easily be fixed you are entitled to a refund of the item. This includes situations where the item has a problem that would have stopped you from buying it if you’d known about the problem in the first place. If the item can be fixed, then the author is required to do so promptly by updating the item otherwise you are entitled to a refund of that item.
So, if I buy a plugin from CodeCanyon, and there is a conflict with a plugin I already have installed, would that qualify me for a refund (provided the plugin author couldn’t find a solution)?