@John Park Tell them that you'll have to make an addendum to the contract and charge extra a month if you have to call ghost busters.

What other ruses do they use to get extra money?

I know if I, find the property, rehab it, and property manage it, I could earn more.  

With little luck, you get extra money each month.

I would make him bear the costs of said checks.If he doesn't pass (or you don't want to add him), serve a notice to cure or quit.You don't want an unauthorized occupant in your rental unit as (at least in NY) they will earn tenant's rights. 

But it definitely makes sense to send a spreadsheet with your offer outlining all the payments, how much interest he will make extra

For example it only took one slab leak for me to realize it was worth the extra $10-20 premium.

Builders Risk insurance, most are fully earned  for either 3 or 6 month policies.

The extra year can be used to dispose house if they don't exercise option.

They may not mind, but I personally would be irritated if my rent stayed the same but an extra person got added into "my" personal space.