Looking for a rental after 13 year, he may be in a bit of shock at the rental prices, but that's his problem.As for damage deposit, you can only keep money for damages that you know he did (ie anything since 2022). 

Yes, many hosts of short-term rentals (STRs) use inventory management systems to track supplies effectively.

Effectively, this wipes out every penny I made from ALL of the investments on their platforms over the past 2 years.Of course there is risk. 

The changes don’t go into effect until November 18th, 2023 but that would be reachable for anyone, even today, if they went under contract with a 40 day close in order to execute after that effective date.Does this apply to 2-4 unit investment properties?

Let them leave, repair any damages they did (from their deposit) and get it rented to the next tenant after you find out a few things. 

We think the tenant might have purposely caused damage to the unit.

The reason for selling is because the home has been a money pit (major tenant damage) and a revolving door (tenants leaving).

As an investor myself, I understand the importance of navigating new markets effectively.

Then we need to do a lot of education and damage control.Needless to say, there are many ethical and investor-friendly realtors out there (especially here on BP :).

From what I have read here, you effectively have 0 knowledge/information.