I think it's important to set criteria in screening tenants for each individual property instead of a blanket policy over all of your properties.
It's important to understand the property value and what kind of tenant you should be attracting. If you have a class C/D property in a less desirable location you shouldn't ask for the same screening criteria for a class A/B property in a great location. I see a lot of people make this mistake. If you have a great property don't sell yourself short. If you have a pile of crap don't expect too much from your tenants.
Setting income requirements, credit score, criminal history, pets, etc. is a great way to set a standard but its not going to always weed out bad tenants unfortunately. No need to beat yourself up about it. Reading people in a 10 minute window is about impossible without major red flags.
(PERSONAL OPINION: If you think vehicle cleanliness is the secret to good tenants you are out of your mind.)
One of my best tenants was someone who needed a co-signer and no rental history. A couple of my worst tenants were high earners, great credit scores, and clean backgrounds.
I'd just tell your friend they better buckle up because they're are in for a treat!