Just a little story that happened recently. After a few non payers I changed my preferences to exclude buyers with 2 unpaid strkes in 12 months which is stricter than it had been before.
Listed an item BIN and had a message saying buyer wanted to buy but ebay wouldn't let them and could I do something? I guessed it was probably to do with either destination or non payment issue but buyer didn't say. They then got back to me to say they had non pay strikes but promised to pay straight away. I wasn't sure whether to let them but was going out so said I would look at it later. While I was out the item sold to someone else (who paid straight away!) Interesting to see that the preferences did actually work but would you stick to your guns or cave if buyer promised to pay? I had been a bit worried about saying no to them as I am a bit soft. But in a way I am glad that someone who hasn't paid lost out on an item.