1. The scammers are more often than not elites who get free checked bags (or at least people who loudly protest that they are elites). It's the poor kettle who has a bag that is a milimeter over the limit who voluntarily checks his bag and pays the fee.

2. It's infantile to argue that you ought to be able to scam a steamer trunk aboard because you don't happen to like the carrier's bag policy. Don't like it, go fly WN and get your two free bags. Some do.

3. This is best dealt with by the GA's, not the FA's. Time to stop the scammers is before they board. Let them board last, miss their flight while there bag is processed. In the end, carry on space is a zero sum game. If you take more than your fair share of it, I don't get any. And so forth. Doesn't really matter to the FA.

Maybe the way to mollify the DYKWIA at the gate is for the GA to give him a small gift as the bag is gate-checked. I'm thinking of a measuring tape.