Ratings usually work out pretty well. As I said earlier, there are intentional ways of deception, playing off of the TD and all the work they have to put in the day of/day before. But often I would say that sandbagging is unintentional...some people just dont know. Sanctioned tournaments really have a low rate of sandbaggin, aside from the Rec division.
I hold that most INTENTIONAL sandbagging happens in non-sanctioned tourneys, and there is the big hiccup in the get-along. Because there is just no way to track that. The upshot to that is that non-snactioned tourneys tend to be smaller, therefore, less prizes/payouts are available in the first place.