Been playing games across the USA for 38 years, and i have seen it all. There are things that go on that you wouldn't believe or suspect. As for collusion, 2 or more players have to get the "mark", which can be any one or more players, in between them, one must have the best hand, naturally, and the other does the raising, getting all they can out of the poor marks. They have thousands of "signals', from scratching their nose, head or whatever, to yawning, a certain amount or color of chips being "riffled", holding a certain number of fingers folded under their hand on the table you name it, it's endless. I have watched a mechanic shuffle the cards and set them up so slick it's impossible to see, and the man behind has to learn how to cut the deck, which is an art form also. You can film it and re-play it in slow motion, and still can't see anything wrong. There is one way to MAYBE catch the "false" cut, you can hear a "click" by an amateur. I once watched this huge guy with large
hands "cold deck" a game, a separate deck set up and put into the game by this brute, his hands were large enough to cover the whole deck and then some, when he "cut" the deck, he took off the `whole deck, and left the set up deck in its place. Bottom dealing, but that will usually give a click too, but unless its pretty quiet, you won't hear it. I have seen things you would think impossible to do done by experts. Even in a casino, there is a chance of being scammed. At home games, i have seen players splash the pot, putting half the bet and getting away with it until warned not to do it again. As they say, trust everyone, but always cut the cards.