Maybe they didn't want that much cash sitting around the house... who knows? I would imagine they're paying cash instead of by check so there's no chance of the embarrassing neighbor check bounce?

:D :D :D :D :D

Accept the money gladly... they're sticking to the original agreement, and I don't see how things could go badly just because they own half the fence.

If you want a little extra insurance on that, draw up a simple "I, the undersigned, promise not to paint, stain, or otherwise modify this fence in any way whatsoever without full agreement of both parties" paper and both of you sign it and keep a copy.

I've tried annoying my neighbors by carrying out a couple of underground nuclear tests and launching a variety of short, medium, and long range missiles. I've had a pretty disappointing reaction so far.
I think I'm going to try barking at them.