Isn’t there an option on the buy-it-now to require immediate payment otherwise it tays up for sale – tick that next time (sorry, I know that doesn’t help with this one!).
Yeah, don’t bother chasing, despite the ‘legally binding agreement’ bs about winning auctions just flog it to someone else. If you did manage to force him/her to pay up, don’t be surprised that it arrived ‘damaged’ or ‘not as described’ (or even worse, a ‘fake’).
But please add to block list and mark as a non-payer. That helps the whole community keep these idiots at bay. You’ll not lose any costs if you do it all properly through eBay.