Aaah , I just noticed that you're account is registered in the States.

I would then contact eBay here explain this buyer is making offers through Private messages looking like an off eBay sale.  This is against the rules,  so eBay should act.

They may,  seeing your account is registered in the States direct you to CS there.  As said,  for an American account rules may be different, we as eBay members here, wouldn't know those rules in the States.

Contact CS if you wish to,  with the link below and try at 8 a.m. as there's more chance of Dublin answering don't contact now as it will replied by automated bot responses.

https://www.ebay.co.uk/help/eua?id=5190

@beesandhoneylondon