only thing i can think of is to post his username all over the neoboards telling everyone to report him
go find more popular neopets themed messageboards (like icedaccounts, tnt has spies there) and pretend to be him and talk about ABing and crap like that. He'll get frozen.
can't you report him for ripping you off for 3 mil? Was it in a trade or for programs, cause I read in neopian times once (I don't know what I was on to be reading that) but yeah it said neopets doesn't like people who scam other newbie users in that sense like someone was selling a rubber sword os skasden or whatever for millions and someone bought it and they got frozen so yeah...
you can also report the person and make up a post that he had on the boards type in something like a racial slur with symbols or something like that
Try this, at the GET ACCOUNT PAGE.. the who referred thingy just KEEEEPPPP posting his un make 30 and earn some money on each ^^