I did the demo but he did the cement board install and prep, tub install, tiling, and shower plumbing and install.  

Even if the occupants destroy the inside, pour cement down the drain, etc., we still won't be in the hole because the margins are so large.

i am real estate investor since last 30 years .i am a dentist

I got a letter tell me to move my car off my lawn (no grass), yet the next door neighbor cemented her whole front yard.

IE For dentists it's American Dental Association.

We have also discussed adding further cement over protrusions so that they are more sloped [less dangerous] and then adding a bit of dirt over. 

If hard money lending is so good why doesn't your dentist do it?

I am 100% sure that a plumber making 80k a year can outperform a dentist who makes 250K in wealth and is not difficult to start from a young dishwasher and become a multimillionaire in his lifetime.

He recommended "cleaning the main sewer, chiseling out cement, to remove vent plate for access into main".

The place was a huge mess and I did take their security deposit which was not enough to cover all the repairs, but at least no cement down the drain or intentional damage to the property.