Seems like a mute point to me.
Unless you have set out in your listing that you will not sell to 0 FB (newbies), then it would seem to me that you are obligated to try and carry thru with the sale, and attempt to collect your money.
Of all the non-paying buyers that I have had - none have been newbies - just people who have changed their mind after making the purchase or have obviously bid without having the money to pay for the item. And, most of them have had a decent FB rating.
A waste of my time - yes - but I just write it off as a "cost of doing business".
Tom