If my auction closed on Saturday (10/13) and I haven't received a payment(today is 10/17), at what point should I send a payment reminder? I don't want to make the buyer angry by sending one too soon. Thanks for your suggestions in advance.
I think I'd send a second invoice with a little note that says "just a reminder". If you still don't hear anything then give it a few more days and send a "are you going to follow through" email. I wouldn't send a stern one for 7 days as that's how long Ebay gives them to pay. JMO
I always send one on the 4th day, since I request that they contact me within 3 days. I ussually say...."Just a reminder, we can not ship your item until we receive your payment." Ussually I get a payment after that.
After the 7th day of no response, I'd open a NPB alert on them. I had to do that twice after sending a stern email which they didn't respond to, then after the NPB alert was filed, they paid. I wouldn't offer it to the next highest bidder until you're totally sure the original buyer isn't going to pay; otherwise you'll technically be obligated to both buyers, assuming the original one says they'll pay.
Do also check your Paypal account to make sure you really don't have the payment; don't just go by the eBay status. I won an auction on the 14th and paid that day. On the 17th, I got another invoice from the seller. I sent her a nice note yesterday with the payment date & time and transaction #. When she checked her Paypal account she did have the payment, the status just wasn't showing as paid in eBay for some reason.