
I suggest asking at your local vets or pet shops for recommendations or other dog owners. We've just visited kennels near us, we used them many years ago but needed reassurance that they were still good. Visiting was by appointment only with your dog.
Their policy is to let dogs stay for a free trial period of a day or night as long as you are available to pick them up immediately if they don't like it! And I think it's a good idea to send them a bit longer each time so everyone is used to it. We have a 2 week holiday booked at the end of the year but Khan is off for his night's trial next month and a weekend the next, and possibly a bit longer in the summer. Pricey, but it's a bit like leaving your kids for the first time with granny!!
Obviously a kennel space is not going to look like your home but IMHO looking for as much cleanliness and comfort as possible, Seeing them with and without dogs in and preferably the size that would be offered to you is a start. Also how are the dogs exercised? Some kennels will only lead walk for a short while but ours also have the option of an enclosed paddock for free running if dogs are sociable.
How do the employers interact with your dog from the start? What is the general routine and what food/treats are offered and do you get a discount for supplying your own? Will they groom them regularly - ours get a bath before going home!!
Hope this helps!