Fred and George's wager on the Quidditch World Cup

[pbeider]

No: HPFGUIDX 33552

I am a newbie, but I've checked the "Mysteries and Inconsistencies 
FAQ" and didn't see this one, so here goes:

Why would the Weasley twins bet all their savings on such a seemingly 
improbable end of the Quidditch World Cup, and how is it that they
WON that bet?

Theory #1: the match was fixed.  But Krum wasn't shown to be a bad 
guy--and why would the twins, of all people, be in the know?

Theory #2: they divined the result.  But JKR has led us to believe 
that true divination is very rare, and they haven't shown predictive 
powers any other time.

My best guess is that JKR didn't consider the ending all that 
improbable.  But since a quidditch game can go on for days until the 
snitch is caught, thus seemingly allowing plenty of time for a 
comeback, how often can it be that a seeker deliberately ends a game 
on a losing score?  And even if that has been known to happen once in 
a blue moon, why would Fred and George bet all their money on it??