When I hear this, I wonder what the point of the sandbagging would be? What are they saving themselves for? If they're worried they're gonna get caught and be locked higher, what would the purpose be of continued sandbagging?
I would have to think the incentive is to be able to have an advantage when one needs. When to decide to actually play their real speed.... sure seems complicated, trying to hide, and manage the the lower skill level, then play well enough to win when needed, without getting caught... in a league that generally doesn't have payouts, or at least not large ones.
I like to keep score for the matches involving players that I suspect are trying to pad their innings.

They have all their defensive shots marked when I keep score.