When you have an unpaid item there is a process which you should go through to protect yourself.
After 4 full days you can open an Unpaid Item Dispute.
After another 4 full days if the buyer does not come forward and pay up you can close the dispute, leave them a strike and claim your fees back.
After this time you can relist if you wish or do a 2nd chance offer. You should never relist until you've gone through the process with the first 'winner'.