I had a neighbor who was extremely messy, and she couldn't ruin her granite either. 

What legal options do you have, if something goes wrong?

It's primarily a legal protection vehicle and should be advised upon by a lawyer in most circumstances.

There are other ways to legally wholesale without a license as well.

It's also good for insurance and legal reasons, because you will need to indicate every adult and all persons, as well as details (like children, pets, etc.), on the lease.  

Since I'm not an attorney and can't give legal advice, I did a little more digging and found the passage below.

I know in California it is legal and the state acknowledges it however it does restrict the finder to basically introducing the parties and they can not participate in negotiations, etc.

Without proper permits, there’s a chance the city may request you to revert any non-compliant additions (like the extra bathroom) to align with code standards.When it comes to refinancing, banks tend to look closely at the property’s legal compliance.

Out of the 20 letters I've sent, I've had 1 guy get back to me and we were in discussions but weren't able to find a price that worked for the both of us.The issue is that I only have a few houses on my mailing list so far (just places I've walked or driven by that caught my attention), and blindly searching every street and address # to see which houses are actually legal multifamily will take forever and doesn't seem efficient.I know the data is publicly available, I just don't know how to aggregate it in a way that would be efficient and useful for blasting out marketing mailers.Are there any websites that can pull massive lists of all multifamily houses in my area?

If a rental/lease contract is a legally binding document...enforced by collecting rent...or enforced by an eviction process if rent is not paid....then can there not be a document (legally binding) for a tenant to sign that would relinquish their rights as a squatter or due process of eviction...