Of course, a specific contract can prohibit assignment, but the law clearly allows it.You cannot advertise a property for sale unless you legally own it.

Also many cities that have ADUs prohibit you from renting out both units. 

Phoenix is not a market that is prohibitively expensive either.

update on this:    the rent control prohibition repeal ordinances (house and senate version) introduced for 2018 in the WA state legislature both failed to get out of committee.  

I believe this is a prime example of why a major tool in screening, background checks, are starting to be prohibited in some municipalities.If he's on a month-to-month lease, then end it once he ends up in jail and unable to pay you the rent.

I don't prohibit them.

You certainly can't prohibit them from owning a gun so I'm not sure there's a truly perfect and practical solution.  

Ken Min , the landlords are just trying to run a legal business but seem to be getting treated like criminals themselves .L.A just started a "ban the box" ordinance which reminds me of this , "Los Angeles City begins enforcement on July 1, 2017 of its Fair Chance Initiative for Hiring Ordinance that prohibits employers from seeking criminal background information prior to offering a job to applicants.

Alternatively, there could be strict laws on employment - only one employee per household, maximum of 20 hour weeks, whatever - but incentives usually work better than prohibitions. 

When I mentioned this thread his immediate response was it's the hosts responsibility to vet the guest, and further, if the rental is less than 30 days you simply call the cops to get them out if they don't leave.We also got into how some CC and R's prohibit rentals less than 30 days but, as was pointed out, is pretty much irrelevant to the host-guest relationship.If you're on top of things as a host it seems easier than being a CA landlord.