I read in Waukeen's blog that he caught bot novices in the Monster Arena Race. Just as I thought. Prizes are really tempting so there is a high possibility that people would really try to bot in that place. If there's a will, there's a way. Someone created lots of trial novices, bet in the Monster Race and transfered all the winning medals to his/her original account. The medals are not suppose to be tradable but apparently, it was. Im not sure, but I think they removed the exchanging NPC's for this medals. Great move LUG :)
This happened in Fenrir server.