If it were, the first thing everybody should do is read their contracts to make sure they aren't going to be paying their opponent's legal bills if they lose... because they add up quickly when demand letters are sent.But based on what I've heard so far, I believe this goes back to what public record was at the time of OP's purchase. 

This product is has a 10 year loan option, a 15 year loan option, or a 30 year amortization option that will balloon in 10 years. 

I bring this up because if you call an agent and let them know you have a preapproval letter then the conversation seems to carry a little more weight.    

This tenant then messaged me to request a formal signed letter if I refuse to let her install the product she wants to use.

I've required rent up front for the entire period, proof of funds to ensure they could cover rent 3x for each month they were staying and a letter from their program administrator ensuring that the students were on rotation and were required to relocate after their rotation was over.

Worst case, give them a LOI (letter of intent). 

Hopefully a letter from a law firm will get them to change their attitude pretty quickly.

One of the requirement that is the most challenging to obtain is a letter from the HOA saying that STR (less than 180 days) is allowed. 

Get an approval letter from a hard money lender or a bank and post a non refundable deposit that in the event the deal doesn't go through the money is forfeited to the foreclosing lender.

Make sure there is a person to get your letters and packages, or stop them for some time so it does not look like no one is at the house.