If the person is willing to give you the money first, there's nothing to worry about.
Otherwise, either Sedo or Escrow.com, their prices are similar.
I usually tell buyers that if it is over a certain amount (usually $500 or $1000) I will split the fees with them - anything less and they need to pay for it by themselves.
It also depends on whether you have a good web presence (website, trading history, identifiable business, use your real name/phone/address).