what I do is this:
as soon as the sale ends, I send an invoice - always. (In case of dispute, you can then demonstrate that you did this, promptly.)
Three days later, I send a message saying; Hi, I invoiced you on (date) for the xxx which you won, but you haven't yet advised me when or how you intend to pay. Please let me know, so I can arrange to send xxx to you.
Five days, I send another reminder saying that they still haven't been in touch, and although I don't like doing it, it's my policy to report items unpaid to eBay after seven days. Please get in touch.
Seven days - I report the transaction as unpaid.
It's rare that steps 2 & 3 don't elicit any response or payment, I've only had to report nonpayment a very few times.
I hope this helps!