Whenever I take our dogs to a different doggy day care (we've been to a few due to travelling and moving provinces) I always drop by for a tour without an appointment. If they are hesitant to show you around and don't want to show you their kenneling area...DON'T GO THERE!
Also, even though its a doggy day care it should be kept clean, tidy and the good ones won't smell. Have a look at the outside area and see if the fencing is good, if the yard is kept clean, see if there are cameras, is it supervised and what is the maximum number of dogs they take per day. Don't be afraid to ask about their cleaning practices and what kind of product they use. Ask for references from a couple of their clients if needed. Since we move often, we ask our vet if they know of any reputable places around, they often know the best! Ask if all the employees have pet first aid and CPR, if they have a vet on-call and what happens in case of emergency.
Sorry if I sound like a freak. I'm very overprotective about where I send our dogs, I only send them to the best...even though they are way more expensive
When we lived in New Brunswick, they went to a pet resort that was acres of fenced in yards (small dogs in one area, large dogs in another, rough players in another, etc), supervised, security cameras all around and was cleaner than my house! It was fantastic! Also, in today's age, any good doggy day care should have a Facebook page or a website that's updated frequently (perhaps even with pictures of your pooch when you're away).