Weight is only checked at check-in.....only ever seen a fuss once after check-in when a woman, who must have hidden her suitcase, tried to board with a full sized suitcase.....think she was Chinese-American.
Seems a very odd incident.....the train doesn't look crowded....and she doesn't look particularly big.....did she actively try to block him and, if so, why would she do such a thing? Strange.
Financial incentives have a limited impact and tend to be short lived.
Financial disincentives have a disproportionate large effect and last forever.
This is not a good move.