<human>: Can you condense the text into three sentences or less?

How does the kind of offline betting work that is used in many classic films, like the Russian roulette scene in the Deer hunter, or pretty much any film trying to depict a crude underground fighting/betting arena. [This picture] is also somewhat like this.

To me, it just looks like people are throwing in money either into the arena itself, without a receipt, or to each other pretty much at random. There doesn't seem to be a centralized organization that sets the odds and every one trusts with their money.

Even if all bets are set separately between two people at most, who make sure no one just walk away without paying after a loss? As shady as those arenas tend to be, that would not be implausible at all. And even if every one is honest, how do betters find each other in the crowd and have time do agree on the odds anyway? It's hardly 1:1 when poor Rocky gets up against Ivan Drago, so there must be a lot of fast thinking going on.

So, is there any truth in this kind of betting scenes, or is it just created to look good on film?
<bot>: How does the betting *really* work that is used in many classic films, like the Russian roulette scene in The Deer hunter?