I'm in the middle of a transaction involving Paypal, haven't used them in years, and I can't recall if they used this idea back then, but it could be something worth thinking about here:
Using an escrow. (is that the right word?)
Paypal has taken the money from the purchasers account and is holding it in escrow until I provide them with a tracking number to verify that I have in fact shipped the item in question, once I do that they will release the funds to me. According to Paypal the buyer has no access to the money, and cannot cancel the payment.
I'm not sure what exactly is involved in setting something like that up here, nor how popular an idea it would be (personally I don't like it, unless I know the buyer I never ship before I confirm receipt of funds, I generally ballpark the shipping cost, or just add 10/20 bucks to the price of what I'm selling, or take the cost myself if it's a small thing) but it could be worth thinking about, at least.
Or the proverbial 'two of you' could invite a third party to act as such for your transaction yourself, if you'd like.
"War must be, while we defend our lives against a destroyer who would devour all; but I do not love the bright sword for its sharpness, nor the arrow for its swiftness, nor the warrior for his glory. I love only that which they defend: the city of the Men of Numenor, and I would have her loved for her memory, her ancientry, her beauty, and her present wisdom. Not feared, save as men may fear the dignity of a man, old and wise." - J.R.R. Tolkien