On the Site Map, find Manage Bidders.
On the Blocked Bidder List, add the seller's name.
(Yes, yes. I know he is not your buyer. Trust me.)
Activate the option "don't allow Blocked Bidders to contact me."
Meanwhile, you are not required to open eBay Messages. When you see the name, mark it Read (without opening) and Delete.
You are not required to open and read emails. Mark Junk or Phishing Scam and delete.
Both buyers and sellers are allowed to Cancel transactions. This is fairly new, but the Seller in particular has repercussions: either a Defect or charged selling fees, I'm not sure which.
Buyers get a note on their Feedback Page for Bid Retractions.
Every contract requires a willing buyer and a willing seller to be viable.