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How does a stranger enforce a friendly wager? Once someone finds out they've been cheated, they'd have no motivation to pay up, and if the hustler had some way to muscle it out of the mark, then they could have just mugged them to begin with..
When someone's mugged they go to the police. When someone loses a bet and thinks it isn't fair, because they wouldn't have betted if they thought they might lose, they don't. And a good hustler won't let the mark find out they've been cheated; they were unlucky, that's all. It happens. Maybe they'll be lucky next time. Double or nothing?
Obvious mugging tends to result in jail-time really quickly. Hustling, and then implying that these two lovely chaps who do not seem to have names may become upset is more borderline. The implication of harm tends to make people cough up, and if they do go to the cops then it usually turns out that it is impossible to prove. Also just implying harm is a lot easier and less work than outright mugging.
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