Heres how bounty hunting / bondsmen work:
BILLY BOB gets arrested
Bond is set at $5000 (bond is what you can pay to go free until your court date, when you are given your sentence)
BILLY BOB doesn't have $5000
BILLY BOB goes to DOG THE BOUNTY HUNTER and pays him $500. In turn, DOG pays the court $5000 for BILLY BOB to get out on bond.
BILLY BOB shows up for court, and the court returns DOGs money to him.
In this case, DOG has made $500 for lending $5000 to BILLY BOB for a few weeks.
BUT
If BILLY BOB doesn't show up for court, DOG can't get his money back...
So DOG hunts his ass down so that he can get BILLY BOB to court and get his money back.