In addition to be cheated in play by an opponent, you can also be cheated by outsiders or people who observe your hand and inform your opponent’s of what you are holding. Furthermore, there can also be a conspiracy among players in a partnership game.
Obviously, you can protect yourself against the first type of cheaters by not letting anyone observe your hand or the hand of your partner. Unfortunately, in higher staked games, this does not protect you completely, since there have been reported cases of observers using high powered binoculars to read the cards and then the person using the binoculars will alert your opponent of what you have.
Outsiders though also work in other more subtle ways. They may come up to you as a “stranger” and after watching the game for a relatively long period of time, suddenly want to bet with you or against your hand. You may see this as a side bet, but then they pull up a chair next to you and you find yourself strangely losing all of a sudden. After you eventually lose a good deal of money, and everyone pays up what they owe, you later see them together talking. It hits you like a ton of bricks; that “stranger” was working with your opponent to get a chance to see your cards. At the time it may have seemed like a natural observer, but really, they are thieves trying to get your cards known to your opponent.
In some of the bigger money games, especially in resort areas in Europe, there may be several outsiders involved. The cheating player may higher several people to watch the play and signal to him as to your holdings. The purpose in having several helpers moving from place to place around the table is to prevent suspicion being directed towards just one of the outsiders helping.
In playing in partnership games, no matter how many players, it is always possible that an individual can be conspired against. It may be that only two of the other players in the game are doing it, in which case they are concerned with having more money bet on the one side than the other, so long as they are on opposite sides. The player playing on the side that is betting the most money will dump his hand so that at the end of the game the larger sum of money passes to the proper side. Also, you may be conspired against by all the players in a partnership game so that, no matter who your partner is, he will automatically dump his hand and cause you to lose every cent you have.
This is very hard to prove, because there is a chance that some of the “signs” of conspiracy are completely accidental. But, if you find yourself losing much more money than anyone else at the table, it is a good indication that you should not be playing with these specific people again.