I would see how he gets along with your dog. Dogs can tell things about people! Also, I would ask:
-how long they keep the dogs out
-if your dog will be walked with other dogs (and if so, how many!)
-where they go (just in the neighborhood or somewhere else? dog park or on the street?) and how they get there
-what time range they'll come in (i.e. could it be anytime during the day, or in between 10 and 3, or what?)
-if they leave a note about how your dog is and whether or not he/she went to the bathroom
-what happens if they are sick or can't come for whatever reason
-how long they keep the dogs out
-if your dog will be walked with other dogs (and if so, how many!)
-where they go (just in the neighborhood or somewhere else? dog park or on the street?) and how they get there
-what time range they'll come in (i.e. could it be anytime during the day, or in between 10 and 3, or what?)
-if they leave a note about how your dog is and whether or not he/she went to the bathroom
-what happens if they are sick or can't come for whatever reason