I've seen this crud a number of times. To deal with it, most houses I play at replace a deck upon request without question. It seems to be the fairest way to deal with this stuff.
Sometimes its very suspicious, other times its probably just someone being nervous, or maybe its from the card bouncing off of a card marker (who knows) but heck if I or anyone spots a tweaked card - get the cards out of there.
You can ask for a card count or a deck switch anytime. Obviously there are limits

You couldnt ask the cards to be counted every hand or a new deck every orbit, but it has yet to be abused....