Look for names that say "want a ho" or something to that effect, or look in the forums. For instance, I had a lvl 15 approach me about it. Her hobo has a 90% record, and she didnt want to make a mistake and attack the wrong person and lose embarassingly. I've taken a few lvl 15's, so I can see her point.

She offered me 1k for every time I attacked her and lost, I gave her 6 go-rounds and she paid me for all of them and gave me a 2k bonus.
At lvl 15 you can go cart racing and make money as well.