A recent discussion at Whirlpool looks at an issue for auction sellers that's become more significant with eBay's prominent (albeit unsuccessful) attempts to push PayPal: what should you do if someone has paid you for postage but you work out that it's easier to deliver the item in person?
While the ethical answer is obvious (ask the buyer if they mind a personal delivery), the problem becomes more complicated if the buyer has already paid for the postage via PayPal (eBay's preferred approach) and then decides to ask for a refund, leaving you stuck with the fees. And is it worth risking personal delivery anyway, since in a dispute PayPal will invariably side with the buyer, not the seller, and you won't have much formal evidence of delivery? The best strategy would seem to be not having a fixed postage fee and waiting to get a delivery address before receiving any payment, but that makes the process of selling more time consuming. Tell us how you'd approach such a problem in the comments.