The challenge is that a good percentage of the homeless population is mentally ill or addicted to drugs.

However I do want to do my best to alleviate his concerns. 

Drug abuse issues too. 

@Chris Springer While you might be alleviating some tax liability somehow (although I'd imagine a city signing off on this would only do so with a tax reassessment which would defeat the purpose) I would say that the appraised VALUE would be much less as one duplex as opposed to two SFRs in the majority of scenarios.  

That alleviated my concern about a failing unit while protecting my wallet from an unnecessary capital expenditure. 

Lots of people want to buy drugs also, just because there is a demand does not make it ok. 

There's hundreds of thousands of people and of course there's every type of person from homeless drug addicts to mult-millionaires.

So, invested her money into apartment buildings and because she got off drugs I gave her a house worth $900,000, today.

Your tenant will never have renter's insurance, which I always require.Air BNB has become something of a problem in a lot of places, due to the constant use of the homes for parties and doing drugs and prostitutes and all sorts of other things you might also do at a hotel, except they are usually located in a quiet neighborhood causing all sorts of issues with the neighbors.

Eviction on file, drug charges, money owed out the butt.