As Pinguicula has stated above, the best course of action is to report the player in-game. I'm afraid that even if you posted an image of the incident on the forums, it would not be admitted as evidence because of the ability to edit images. Furthermore, implicating a player's username is against the 'no shaming' rule of the forums. Again, best thing to do is to report them in-game.
Well.. Vlumondoxa is correct. The forum rules don't allow for reports of misbehavior or rule breaking on the forums for various reasons. Often that's called naming and shaming here. If a J-mod takes action against the scammer it will be because of your in-game report. Reports posted here aren't needed.