You can only offer second chance if there was more than one bidder. It appears in the dropdown at the right of the sold listing. It relists as a buy it now that only the second highest bidder can see. You set the time limit for however long you want to give them. If they don't take up the offer, it just ends like any other item. 

OP, definitely open up non payer disputes against your non payers. Don't let them get away with it. Plus, as mentioned, you get your fees back. Once they have 2 strikes to their name, they find they are restricted from buying from a lot of sellers. If you are planning on selling more stuff, let us know and we can give you instructions on how to set blocks up, so people with 2 or more strikes can't buy from you.