I would treat it like a damage repair for something broken and bill them  this time around based on improper use like throwing something into the plumbing lines. 

The cabinets took a little longer to install because you have to assemble them but if anything gets damaged I can just replace the small peice of the cabinet and not the whole thing like most pre-made ones.

If I were you, I would show some actual returns from C class and their inherent headaches & unexpected costs from tenant damage and vandalism, etc vs projected returns.  

I did give them half of his security deposit back but he claming he wants the rest because a piece of furniture was damaged from a water leak and its costs $400.

I let them know that service calls for heat/ac malfunction or damage due to clogged filters or missing filters will be billed to them, so keep the filters changed as necessary.

We offer a finder's fee on deals we close and can help people with homes in danger of foreclosure, with water or fire damage, or who just need to sell quickly — no renovations needed or questions asked — as long as we get the deal before it's listed on MLS!

Often it will say something like "Sellers sole recourse is keeping the earnest money deposit as liquidated damages." 

He came home at 3am, drunk and kicked my door in and damaged all my screens.

Depends on the extent of the damage.

They will prevent more costly repairs from moisture damage.