After 4 days you can cancel and relist, select the reason as 'buyer didn't pay’ (eBay works in 24hr cycles so the option won’t be available until 4 x 24hrs have passed). There’s a link on this eBay page:
https://www.ebay.co.uk/help/selling/getting-paid/resolving-unpaid-items-buyers?id=4137&st=12&pos=1&q...
The non-payer can't leave feedback and gets a non-payment strike against their account, which sticks to it for a year.
Don't be tempted to leave feedback for a non-payer - it can only be positive and will enable them to remove the strike they receive.
Set your Buyer Requirements to block bidders with two or more non-payment strikes in the last 12 months and add them to your Blocked Buyer List with this link:
http://offer.ebay.co.uk/ws/eBayISAPI.dll?BuyerBlockPreferences
