As a reminder that there have been and probably are dirty refs out there, this story on Tim Donaghy is an interesting read:
http://www.espn.com/nba/story/_/id/25980368/how-former-ref-tim-donaghy-conspired-fix-nba-games
This nugget from the story:
"If you looked at the stats," said one gambler in The Office at the time, "you could see he was calling more fouls on the team he bet against and less fouls on the team he bet on. That was obvious."
Said another: "Did I assume he was fixing the games? Yeah, I did. But I didn't give a s---, because it was great information. From 2003 to 2007, we didn't miss a game. Any game that he reffed we had a wager on."