Look at a Tenant's car when choosing applicants...

[Alan Asriants]

When screening a tenant, don't just look at a tenant's application and credit score

Their application will tell you a general idea of whether or not a tenant is qualified, but it won't show you how they will take care of your property.

When I look at tenants, I try to see the car they drive. I don't care about the make, model, or year, I only care about it's condition. 

The car's condition is a sign of how they will treat your property. Is their car clean? Messy? Lot's of damage and scratches?

Another thing I pay attention to is:

How do the prospective tenants walk into the place?

Do they barge right in? Do they ask to take off their shoes? Do they formally greet you?

Are they constantly pointing out problems and asking you if things will be addressed? (Negotiating before even submitting an application about nit picky things that don't matter)

What do you guys do to screen your tenants besides an application?

[Nathan Gesner]

Quote from @Alan Asriants:

Their car and behavior may present some red flags, but you should never approve or deny someone based on the condition of their car, their ability to maintain eye contact, or the firmness of their handshake. What if you reject someone for a dirty car and it turns out she's a hard-working single mom that doesn't have time or energy to maintain her car because she works her tail off to pay bills and spend time raising her kids right? 

You're subjective discrimination is likely to get you into hot water with Fair Housing. Your approval or denial should be based on objective criteria that identifies the level of risk a potential renter poses to your property, income, time, or sanity.