as a buyer its a convenience for me.. i don't have to waste my time going somewhere to buy a money order. and i also don't have to wait for the MO to get to the seller and clear before my part is shipped... i gladly use paypal to save me from waiting...
just bought a bracket from a guy on facebook the other day.. used paypal and gladly paid the fee. part was here today. if i bought a MO then the part would still be in the sellers hand and not to me for probably close to a week from today.
