If you get non paying bidders, go the route of an official non payment dispute. I liked tippy's wording-do other sellers a favour.

It isn't your feedback that will help them, but more the strike a non payer gets might eventually help to block them from buying from other sellers for a time.

As for feedback, any buyer who pays for an item can leave you feedback, even if they were a bit slow off the mark to pay and needed a prod. With luck, that particular buyer of yours won't bother with feedback or will not give neutral of neg feedback. If they do, you can give a factual reply eg buyer took 8 days to pay.

Basically, if any buyer gives you grief in a transaction, you'd be better off giving them no feedback than any feedback that involves awarding them a green dot.