I'm just playing a sequential game where two people are deadbeating right from the start because they started out with bad holdings.
As it is, deadbeats don't lose anything and the worst you can do to them is give them negative feedback, but how about this:
People who deadbeat from the start of a game lose points, too. These are distributed among ALL the other players in the game, not just to the winner(s).
It's only an idea I just had but I feel that would take care of deadbeating in no time at all.