If you tell the constable that you are concerned about damage, they may talk to him about leaving responsibly.If you are concerned about violence, have a means of defending yourself and let him know it.

You should bill them both for the damages, take pictures and go to court.

most contracts your 5k is your liquidated damages in most contracts. .. so snag that fire the agent and find another buyer if 13k is that important to you.. for sure not worth hiring an attorney for. 

Selfishly, being able to respond fast, mitigates damage to the property (frozen pipes, mold!)

. --- We haven't seen a S8 inspection report in over a decade that required a tenant to fix damages they obviously caused.

In our rental agreements, we use the security deposit to cover any damages once the lease has ended.

The Landlord will verify that the rental is empty of all personal belongings and trash and that there is no damage beyond ordinary wear and tear. 

If they damage your property here, you're SOL!

Whats more, there was damaged equipment that costs about 3k.

Sounds like an unreasonable seller and the most likely reason for them not wanting an offer with a financing contingency is the property is in too rough shape to get financing on it (structural damage, fire damage, etc.) or won’t appraise anywhere near asking price.