I'd like to confim:

If two players play an in-tournament game and say “whoever loses buys the winner a booster”, that is Wagering.

However, if two players play a Magic game after they're done for the round and bet on this game, that is legal.

Correct?

It is not against the Magic Tournament Rules or Infraction Procedure Guide, if that's what you mean. We aren't concerned with a person's actions that aren't directly related to the tournament and its integrity.

It may still be against the law or the store's guidelines, but that's not something in which we necessarily need to get involved. This would be the same as the players playing a game of poker between rounds. It doesn't matter that they are using Magic cards.

What Josh said - it may not be legal, but we'll probably never know, and enforcement is next to impossible. What players do outside the constraints of the tournament (and outside the venue, of course) is pretty much out of our hands. (With the obvious exceptions of when they post something in a public forum, admitting how they broke laws or rules…)

d:^D