WHAT AM I ALLOWED TO DO TO VERIFY SOMEONE ACTUALLY NEEDS AN ASSISTIVE ANIMAL? WHAT DOCUMENTATION CAN YOU REQUIRE? CAN YOU CONTROL BREEDS?

You may absolutely verify if someone needs an assistive animal. Ask for documentation substantiating such need from a health care provider or agency. The breed of assistive animal should not be of concern to you upon receiving documentation of need. You may, however, obtain documentation that the assistive animal has in fact been trained to provide such need. I would assume that such documentation has already been given your tenant by the trainer or training organization.