Jim
Try and exchange any contact details with a seller or buyer in a message via eBay
UK
before an item has sold, and their snooping software detects email addresses and deletes them, and you may also get a threat from them to shut your acount down either temporarily or permanently as they say their T&C are breached, and you are trying to sell outside eBay.
Several years ago I had someone local wanted to view an item (a lathe) before the auction ended so they could decide whether or not to bid after checking the condition. Perfectly reasonable you might think, but, eBay repeatedly blocked the messages, blocked my account, and when I took it up with them, wouldn't accept my explanation!
What doesn't appear to get detected (yet) is to photograph your contact details, and send them as a message attachment.