I think one could argue that the odds are distorted due to having to take into account tanking behavior and this makes room for rigging opportunities. Also, a team's desire to tank is not always clear cut. In the case of Chauncey Billups, the Blazers didn't start out the season with the goal to tank, but towards the end of the season they may have decided to tank at some point. From the outsider's POV, we don't know when exactly the team decided to tank to increase their draft odds. But people closely affliated with the team, in this case the head coach, knows and can share this insider knowledge for gambling purposes.