What about playing poker with a used deck? I've played in the same poker group for over two decades and even in this social game it's customary to have two unopened decks when you host the game. We're all good friends. Do we really think a guy who brings out two used decks (as has happened very infrequently when someone "forgets" to buy new decks) is doing so because he's marked the cards? I don't think so, yet everyone is queasy when used cards are presented.