Some sellers on other sites only accept money orders. I bought one coin like that. The power is in your hands that way and there is no worries about filing a claim. There is no record of funds ever being received with cash but with money orders there is a receipt and a paper trail. I think with a money order it is much more difficult to file a claim.
I'm not entirely sure you even could short of suing someone in court. Paypal would be out of the equation since you have to use them to get their protection, and you start getting into shaky grounds when it would be an actual charge to you from ebay as opposed to returning funds. Aside from not having to pay the electronic money fees sellers love money orders because you really don't have to worry about someone filing a charge back after getting the item.