yeah you are right if they dont want it at they wont pay the deposit either,but you get some people with good intentions who lose interest or get a better offer so the deposit if received before this happens will help keep them motivated to complete transaction,
i sold a hj sedan to a guy in qld once he paid the deposit and never got back to me and i couldn't get a hold of him so after 3 months i just resold it, i was happy with that