Open the unpaid dispute (which you have done), let it run it's course and if they do not respond you can close it and leave them negative feedback.
If they do not respond by the time you are able to close it they forfeit the ability to leave feedback so they cannot retaliate
(see eBay site)Making direct contact gets personal, and un-verifiable, keep to polite reminders via contact buyer so it is all traceable.
When closed you can also claim back FVF fees and then 2nd chance offer.
Do not 2nd chance offer before the dispute is closed or you will pay FVF again and cause feedback problems.
Beware a cornered buyer may turn nasty and even claim non-delivery, generate a chargeback fraud and leave you a negative for being a bully (even though you were not), so it is not worth chasing via personal contact you could come off far worse.
If the bidder got carried away and realised that then he may cause you grief. If the item was worth that amount relist after the dispute is closed because bidders who lost out will bid even fiercer next time.
I also find that 2nd chance offers are rarely taken up because bidders would rather try and get it cheaper by starting again.
A refused 2nd offer also loses you your insertion fee credit item unsold on first attempt.
I hope that helps.
