If someone plays a game with me with this, I'm totally going to be spending time between every turn in the Dev console figuring out a one-liner to reveal as-yet unturned cards...
Flip the card really quickly (single animation frame), get data, boom. Maybe you'll get noticed, but probably only by someone who's equally sophisticated in detecting tricks.
Cryptographers are really interested in card games as a model of information problems, so there are pre-existing algorithms for how to do stuff for card games in which different players have different information about the state, but everybody can prove to their satisfaction that the others aren't cheating - without a trusted server at all.