Best way is to talk to his/her friends. Talk to their family. Talk to their last (not current, who may want them out) landlord. Talk to a professional contact. This is where 3-4 references, phone #s not letters, come in.
Talk to THEM for 15 minutes. You can usually tell who’s who, and if you have only a few properties, you have a lot more time to vet prospective tenants than if you manage 10 100-unit apartment houses.