1 Renters seem to be a great potential menace.  Obviously most of them are fine, or the concept would disappear, but you hear enough horror stories to sometimes think nobody should be rented to without a background check or something.

2

RickC:

The last couple of places I've rented, I've had to sign a release for the landlord to do a background check.  (And a credit check)

3 Had to rent my home in Michigan out, after seeking employment points south in 2008. After six months the tenants trashed the place and skipped town, and I had to spend most of the rent they'd paid repairing it.
Amazingly, it wasn't a matter of, apparently, deliberate damage. They just had no concept at all of how to live in a house. Didn't recharge the water softener, so the showers and other fixtures were brick red, kept dogs in the basement and never cleared the poop, things like that.
The interior of the house, literally, was a midden.