True, but the OP said the item had "substantial value". Most first time ebayers won't go for expensive items.
Make sure in your advert, you clearly state that you won't post abroad with no exceptions. That prevents a lot of zero bidders who happen to be scammers.
I'm selling something on eBay of substantial value ...
If it was me, I'd cancel his bid. However you have mentioned the item is worth a bit.