This could be something that's completely case by case, but I was curious if there might be some official regulations or whatever.

Also, if something really bad happens (house burns down, tenant gets electrocuted and dies) things will be much worse for you when it comes out that the setup was sketchy and didn't have any official stamp on it.

The zoning enforcement officer shall require that a declaration of the accessory family dwelling unit for the family member, or members, and its restrictions be recorded in the land evidence records and filed with the zoning enforcement officer and the building official.

I had them draft an official letter to the neighbor and the HOA. 

This would be my first official unit in my portfolio.I would like to manage it myself if possible as to keep my cash flow higher.

I sat in the car and wrote out my contract on a pad and explained that we were officially under contract until I had my awesome realtor create one.

If I get a handful of people interested in going, then I'll make an official event on the events page!

I am stuck officially and have been for well over a year.

IIRC WA did pass in the last few years statewide clarifications that if occupants of a property could not produce documentation of rental agreement they could be treated as squatters and removed by the sheriff without the same eviction process as for an official tenancy.   

By the way this is my first official investment I have been a accidental uneducated landlord for 5 years.