Does it even have to be an incomplete item... I would imagine that most items 'returned' under the distance selling act end up sold on as 'b' grade items. If I recieved a 'new' item where the packaging had 'obviously' been opened, I would not accept it.
Look at LCD panels.. people return them because there is a dead pixel... so you get an LCD screen where it has been repackaged, and the odds are you got someone elses 'rejected' screen.
There are normally telltale signs when a package has been opened.