I believe they are cracking down on scammers, so scamming somebody like that is against the rules, and you shouldn't have too much to worry about.
Still, though, it's probably not a good idea to set yourself up for something like that if the dude seems shady.
Also, make absolutely sure you never put anything of worth up. Always work through REQUESTS for valuable items.
I.E. you post YOUR rocks for the loom point buyer's +2 item. Then you ACCEPT the loom point buyer's REQUEST for rocks in exchange for the +3.