The most important things you need to know are their social, dob, current and previous addresses with rental amounts and dates, including landlord names and numbers, where they work, how much they get paid, general yes and no ques about rental issues and criminal issues (many will lie here so it is easy place to get denials for), emergency contact info, drivers license no, phones no and the authorization section that you will need to fax to apartment buildings to verify rental history.

Some income may not qualify, seasonal jobs that are not regularly performed, part time jobs that are not performed on a regular basis, employment income received from a job or line of work less than two years, child support payments that are not paid through any court system with a history of on time payments.I would insist on saying that "Compensating factors effecting credit, income, employment and criminal histories will be considered to the benefit of the applicant".

You'd have to establish that they're "at fault" (i.e. failed to pay rent, breached a material term of the lease, engaging in criminal activity on the property, etc).  

My written warning reminds them it is illegal, criminal behavior is grounds for termination, and that they will be charged for any damages or additional cleaning required.

I believe its already banned seattle or statewide to consider eviction or rent debt if it occurred during pandemic,  and you can't screen for criminal background in seattle prior to that.   

Do credit, criminal, and eviction checks.

running a credit/criminal background check doesn't work if you have no idea how to use the information. 

I have requested a criminal investigation into Harbor Funding and have the U.S Justice Department and FBI involved.

You definitely want to do a criminal and credit check like you would with a new tenant.

You should also check to see whether or not they've had any criminal or civil court cases brought against them.