Writing a payment reminder to a forgetful eBay customer can get sticky. You don't want to aggravate the buyer, but time is wasting, and you could spend this time reposting your item. When writing a payment reminder, you need to be firm but pleasant. Real things can happen in people's lives. Family members get sick, and people just plain forget. Perhaps your payment fell between the seats of the car on the way to the post office.
When you honestly forget to send a payment, nothing is more humiliating than someone debasing you through e-mail. So remember that people do make mistakes, and check the winner's feedback before you send the letter. If you can garner from the feedback that this winner has a habit of not following through on bids, you can definitely be a bit firmer in your wording. Always set a clear deadline for receiving payment, as shown in the following letter:
You won an auction of mine on eBay last week for the Greatest Sales Man book. Your payment was due yesterday and it still has not arrived. Perhaps sending payment has slipped your mind considering your busy schedule. I know it can easily happen.
Please e-mail back within 48 hours and let me know whether you want to go through with our transaction. I'd like to put the item back up for sale if you don't want it.
Thank you for your bid,
How firm you choose to get with a nonpaying bidder is up to you. Some people who tend to overbid are indeed violating the contract to buy, but legitimate reasons might explain why someone hasn't followed through on an auction. You must decide which method to take and how far you want to stretch your karma (what goes around comes around). Assess each case individually, and don't be hasty in leaving negative feedback until you know the whole story.