With that said as @Mitch Messer go back to the drawing board with the screening process and draft a new agreement including the boyfriend.  

Use long screws, screw the board into the studs, then attach the towel rod onto the board.

Obviously I'd prefer to leverage the high-density designation over the lower-density one, but is there any norm for how a zoning board will rule on this?

I'm with you in that I conduct ALL my business above board. 

You can try going for contractor board consumer route, next contractor bonds, next civil court, maybe criminal.

You could get your deposit back, you could lose your deposit, you could be sued for specific performance, you could be fined by the real estate board for brokering without a license, or you could go to jail for fraud. 

I would get several cans of the low expand foam for doors and windows (brand name of 'Great Stuff' is just one of them) and spray foam complete entire window bay from top to bottom.If that stays dry thru a couple cold or wet spells drywall over this area with either drywall rated as moisture proof,,,mold resistant,,, or even use cement board tile backer(that should NOT harbor mold)...Paint to match

and the front doors looked like dart boards  LOLWhen U drove around town the worse looking props were his LOL.. but at the end of the day I suspect when he died his props were worth north of 50 million. 

I'd go to the condo board and tell them what happened.

You need to join the local board and join a local brokerage.