So, I am not sure how I would pursue damages and unpaid (2 months rent) if I wanted to.In hind site I should have kicked them out, but I didn't - lesson learnt.  

Very certain we overpaid, but it was a dire situation where the old one broke and had caused water damage and the tenant didn't notice for a month... 

You are going to want to file a claim against Person B and hold Person B accountable for the damage.

While this isn't common, I have know people that bought their first rental and when tenant moved out, had caused close to $20k in damages and skipped town after one year of living in place.  

I offered a reply asking about damage to gutter.

If they choose to stay, let them keep smoking because the damage is already done.

This is not even considering any damage that could be done to the property during the ownership of the buyer. 

What happens if there is damage to your property and there is no security?

For a while I just gave him the benefit of the doubt that he was too busy, but that just doesn't make sense especially when it started causing him so much damage. 

I agree that the drainage issue is something that you may want to look into correcting asap because it could result in mold or further damage.