As long as you don't disturb those things, most of them will be grandfathered in.  

Try going to your local auctions and observe the buyers and position yourself to talk to them after/before the auctions, do not disturb them during. 

Maybe see if they have a criminal record of fraud or public disturbance or anything. 

Landlord claimed tenant had not paid rent and was violating the lease by having an unauthorized occupants and by creating disturbances whereby the cops were called to the property on several occasions.

Do you think the possible mentally disturbed man is your tenant?

I have one section 8 tenant and she has let an unauthorized occupant stay in the apartment.This unauthorized occupant is causing a lot disturbance to the other tenants in the building.When I talked to her today about this unauthorized occupant in her apartment, she simply refuses to address this problem with me.

That could also reduce the risk of the potential tenants that could disturb neighbors..  

I would have also negotiated that the foundation repairs be done before closing and that any repairs resulting from the disturbance be negotiated at the time of repair or just covered by the seller.

Sheriffs office showed up to avoid any disturbance, changed the locks, did a quick inspection and gave them back their deposit.

Familiarize yourself with local lead paint laws and be aware of the extra precautions you must take when disturbing it.Same with asbestos - it's amazing how widely used that stuff was.