A neighbor wants to buy part of my lot. OK, what next?

Point taken. Truth be told, I’ll probably just take whatever he offers, unless it’s insulting. The net loss to me (assuming this doesn’t significantly affect my resale value or get me into trouble with my town) is that I have less to mow.

The main issue with this, in my mind, is that the realtor is then working for the neighbor and has their best interests in mind, not necessarily yours. To that point, if the neighbor’s realtor then comes to you with a supposedly “fair” offer, you don’t have to take it. As I said upthread, the neighbor should expect to pay above market rate for this, not necessarily what is “fair.” (And what is “fair” is in the eye of the beholder regardless.)

Do you have a mortgage? I’m guessing the bank would be extremely interested in any actions which lower the value of their collateral.

Nope, owned free and clear.

Not quite the same situation, but there was a person in Rhode Island a few years ago who bought the empty lot next to theirs, then subdivided it so they could add a garage on their own property.

Unfortunately for them, the Town then changed the rules on minimum lot sizes to build a house. Existing houses were grandfathered, but this property was vacant, and so the smaller lot became a non-buildable lot, causing its value to plummet.

The owner then sold the lot. The new owner—who knowingly bought a non-buildable lot at a bargain-basement price—was sure they could get an exemption from the town. They couldn’t. They were not happy. They sued the Town and lost, then cut down all of the trees and painted the stumps garish colors to protest, which made the news.