Service Animal question

[Lois S.]

I have a SFH for rent. It's been advertised as a No Pets property.

During a phone screening, caller mentioned a family member who doesn't currently live with her, will be moving in with her because he has a disability. Did not state what it is, but he does travel to work currently.  Caller also stated he has a 'service' dog, which had belonged to his GF & the dog was trained to 'hear' for her.  (trained for the GF, who is deceased)  

So, I get it, he's probably fond of the dog, but the dog wasn't trained for him.

Assuming all else checks out, what would you do?

Thinking of an in-home visit to check out housekeeping at the dog owner's current rental, or just deny on no pets policy.   But hate to open the whole 'service animal' issue