What is the penalty for not marshalling?

[sim]

Was at a race event yesterday where the fastest driver won convincingly in the first two A-mains (1st and 1st) so he sat out the third one, and then stupidly neglected his turn marshall duties. There was some trackside talk about him possibly losing all the points from one of his best mains, but in the end, the race organisers concluded he was still the overall winner.

What are the rules for this at the big events where you guys are?