Check local regulations on maximum number of unrelated people living under 0ne roof. 

For STRs, focus on areas with robust tourism and flexible regulations.

Not every state or city mandates that any landlord has to accept Section 8, because the landlord has to not only subject their property to Section 8 inspections, rules and regulations, they also often have to separately arrange for the tenant to pay the non-covered part of the rent and can face difficulty evicting just based on that.

Not following the requirements (within Seattle city limits will likely have additional rules and regulations) opens the seller up to liability.Additionally, the seller always has the option of offering "cash for keys" arrangement but be sure that no funds change hands until after the property is vacated and locks are changed.John

Narrow down your location based off of your comfortability, budget, local property owner regulations, and rent to price ratio, and you'll be building a portfolio in no time. 

The final wild card is government regulation and how it could affect the investment.

It is the worst because you need to understand the patchwork of regulations across the state, which can vary down to a neighborhood by neighborhood basis.

The regulations around what properties you can add Tiny homes too was cumbersome.  

Ramsha - most of the regulation for a STR is controlled by the neighborhood HOA.

Maybe he does file a nuisance mechanics lien (whether he can and precise procedures) will be dependent on local law.