My city once sent me a very nasty letter threatening the wrath of various agencies if I didn't terminate my illegal STR immediately and send them proof.After cleaning up my shorts I politely informed them that their google street view was one address off and that my property was completely legal.That was the last day I ever considered flying under the radar.

They threatened to place their own insurance if I don't comply - which I have for now because "their" forced policy was $2,500.

@Christopher Phillips so far we are just waiting for the escrow company's next move as they've been silent while buyer's attorney has been threatening to sue anyone who viewed this contract.

Long story long, she is threatening to put a lien on my rental properties if I don't pay the whole thing in full.

You could threaten them at that point and use a M2M but pigs never change.

After informing them of the reason, they are now threatening to sue us.

You want your lawyer to be better than the other lawyer.BTW I get threatened to be sued so often that usually it does not raise my blood pressure one iota (there was an exception last summer as it was personal). 

If specific performance is an option in the contract, sometimes an attorney letter threatening that action will get them to the table, if they think you are serious.

They had a real estate agent 'helping' them and she is a nut, threatening to send someone to stand on my doorstep and calling all day long.

I wouldn't put it past B to threaten me with a small claims court suit over the money, and I'm nervous that some loophole or nitpick detail is going to bite me in the behind.