How to handle/investigate RMT in FC?

[BiBi___]

This guy with no crafting classes, buys up i110 battle gear for his bard, asks me to meld it. I asked him where his gil came from, he said his friend played since 1.0, then I push the name of his friend out of him. What should I ask this friend of his, when I see him online?

P.S. Also can't RMT gil buyers come up with better stories? I always hear this "friend" story.

edit: Anyone have methods or previous experience, of finding out whether a player has gotten their gil through regular gameplay, or illegitimate means? If the latter, we can boot them from FC and slip a note to SE.