How deeply do you look at credit risk?

[Albert Johnson]

Hi, I have an upcoming unit that will be available. My current tenant is saying her son wants to rent one of my units to be closer with their kids. The current tenant says their son's credit score is really low because of his divorce. 

However I have a pre-screening rule of having major concerns such as bankruptcies, bad credit, crimes against people etc..  My minimum credit score I will accept is 620. I mentioned this to other tenants who were interested.

However, the tenants mom is saying they can co sign for them. I have never done this with another tenant.

So how deeply do you look at credit risk? And your thoughts on how to proceed?