Many times the plastic/rubber flap inside the tank doesn't close properly so the toilet runs and runs. 

The problem isn't the additional hot water usage, it's the undersized hot water tank.

Tenants who are the "complainers," can smell weakness like a shark LOL.  

@Dana R.The deal is tenant is to leave the unit in the same or better condition than they found it right.....They didn't.Doesn't matter who gets the knots out if that's how you do it, but charge them for the time spent dealing with the issue.Had a move out where a toilet tank lid was broken.

After evicting her for falling behind on rent, I found that she had stolen the microwave and poured sugar in the lawn mower's gas tank.

@Steve RiversHey Steve, at one of my (12) unit buildings, the hot water tank went out...the parts took 1 week!!!

Hot water tank (check for leaks), furnace, smoke and carbon monoxide detectors all confirmed to be working properly.

I've done million dollar loans (not my money being lent) for people with 800 FICO scores that I wouldn't let borrow a pencil (if I owned the pencil) for fear that they'd steal it (but, again, if you want to pay me to lend someone else's pencil... sure, here you are).Conversely, I've had to say "no" to people that I would let marry my sister and lend my personal car to in exchange for a full gas tank with no hesitation, because of a stupid FICO score thing.As landlords renting out your own property that you actually own, you are strongly advised to throw out the FICO score and look at & understand their credit history. 

You are right no one trusts a landlord, Landlords are not a trustworthy segment of business society, akin to the loan shark business. 

.-  Medical collections can tank a score.