When I was a landlord, I paid careful attention to the vehicle they drove. If it was clean, shiny, and a later model, I already knew two things: they knew how to take good care of things and were financially responsible enough to finance a vehicle. Hope this helps.
I'd be careful renting to younger people or students as they are much more likely to party, break stuff, have lots of traffic in and out, make more noise etc. Clearly there are responsible students so you ready do have to go with your gut and just hope for the best.