If you are concerned about the feedback thing, send the buyer a polite message explaining that ebay have already charged the commision fees to your account and if payment is not made in the next day, you will need to open a non payment dispute to get the fees back. Alternatively you can send the buyer a cancellation request if they have decided they no longer want the item. Remember to select, the buyer requested the cancellation for your reason in the cancel process. This is all fairly dissarming and gives your buyer a couple of options. Better to have a stroppy buyer opt out, rather than put up with their rubbish. Lifes too short.

Personally I dont muck around sending messages chasing buyers payments. I give them five days to a week or so to pay and then just follow up with an unpaid item dispute. This saves the agro of getting non paying buyers offside, as I simply dont enter into communication with them. I have never copped a neutral or negative feedback yet using this strategy.