Handle problems discovered by either you or the customer.
A diplomat is a person who can tell you to go to hell in such a way that you actually look forward to the trip.
–Caskie Stinnett, 1960
So you're packing up an item to ship to a customer, and you suddenly discover a scratch, scrape, hole, discoloration, or missing part that you hadn't noticed and hadn't mentioned in the auction description. Sure, you can pack it up, ship it, and hope the bidder never notices. But he will, and you know it.
The best approach involves a quick preemptive email to the bidder, like one of the following:
"I just noticed a nick on the back of the item while I was as packing it. Let me know if you no longer want it, and I'll refund your money. Otherwise, I'll ship right away."
Give your customer a way out. In most cases, if the problem is minor, the customer will still want the item. Not only will this note make you appear honest, but your customer will have a more realistic expectation about the condition of the item, and less reason to return it when it finally arrives.
"While packing up your item, I discovered a flaw I hadn't noticed when writing up the auction description. I've attached a photo. If you still want it, I'd be happy to send it to you along with a partial refund. Or, if you're no longer interested, I'll refund your payment in full."
The photo gives the customer additional information with which ...