They don't even realize they're doing it.
These markings are typically from people peeking at their cards while having a chip on top as a card protector, which makes the dent. People have been saying it's the shuffler for ages, but I highly doubt it. I think the chances of someone trying to take advantage of this was close to zero at this particular table but it seems the opportunity was at least there. This was basically laughed off as the room getting full use out of each deck. One player mentioned it to the dealer who claimed that it was only on the front of the cards due to the shuffler, though marks were clearly visible on the backs too. Is anyone concerned with the condition of the decks they use at MGMNH? Was playing last night and one of the decks was horribly marked up.