In terms of the weekly tournies I don't think that sandbagging is a real issue. As said before the payout is so small that no one really cares, does anyone really check to see if they won those 14.37 credits after playing.
The real problem is in the MPC. I can't play these but friends of mine who play them talk about the sandbagging issues here. Heck if you bet 500 credits and win that makes up for 50 weeks of trying to win in a weekly tourney. WGT has too much of a stake in these to limit things, they get 10% juice on both sides, they want as much play as is possible in this.
I have never understood why MPC is allowed on this site, it is gambling pure and simple with the bookie being WGT except that unlike in Vegas, the WGT takes 10% juice on both sides of the bet.