For example, a doctor wouldn't refuse to treat a serial killer, so transitively it would be bad business for a landlord to refuse to rent to a serial killer.Do you agree with that statement? 

Your tenant with heart issues might be able to find a doctor to classify him as "disabled" or "handicapped".

When he requested receipts, the landlord faked them and it was obvious they were doctored. 

If it's not obvious, then you can ask for proof that she is disabled - not the details, but a document from her doctor or psychiatrist that just says she is disabled will do. 

Also, there are also a lot of young Doctors ( read medical/dental residents) who often move out of state  just for the duration of their residency.

We rushed over to make sure and also are sure the parents took him to the doctor.

Your doctors office. 

Doctors said that.

I asked if he smokes, he said his dad smokes, the doctor is ordering him to quit, but he won't.

That can be tedious but the only way.Also ensure that your doctor or heath facilities you visit or plan to visit takes that health particular plan, before you sign up.Unfortunately, no one in either parties elected or running for office been able to fix health care in the US.