However to do criminal background checks and credit checks, what forms do you need them to sign off on?

This occupant has to have somethin on the ball to be in a house of that value, he's no skid row bumb, usually they won't get into criminal behavior destroying the place, they will sit as long as they can but I doubt the sheriff will be dragging them to the curb. :)

We're at the point where after ten years of renting out grade C apartments in a low rent town,  we know more about eviction law in our state than most lawyers do.The corollary is to screen well, but if you're dealing with low end rentals, anyone willing to live there will have bad credit, so what you're really screening for is past evictions, lawsuits, nuisance suits by the tenant, court judgements, and criminal behavior. 

It sounds like you may have either a credit criminal, or someone who has no real ability to repay, both of which could, and should, have been screened for.

.: Sorry, but 550 credit rating is for criminals.

A recommendation for best sites to screen tenants (background, criminal, credit, etc)Any information would be greatly appreciated.

Dept. of Justice has advocated to sellers/buyers for many years.

However, landlords may terminate a month-to-month tenancy with a 20-day notice if the tenant has violated the terms of the rental agreement, committed a nuisance, or engaged in certain criminal activities.Under the state's "just cause" eviction law, which applies to tenancies in Seattle and some other cities, landlords may only terminate a tenancy for specific reasons, such as nonpayment of rent, violation of the lease agreement, or a landlord's desire to sell or occupy the property.

The so called Housing Justice Project might give you some info also, but also not up to date.

Just be sure to get one that gives a credit, criminal, eviction check.