You also have to go with your gut feeling. Once you are happy with the physical aspects eg the place is warm, clean and dry - you have to be happy that yuor dog will be happy there coz if not you won't enjoy your break and will fret.
See how they respond to your dog and ensure you can have a trial session first. Make sure they know any quirks that Holly may have - including the barking and see how they would deal with them - don't forget grooming. I have had kennels say to me - "oh - so you'd want them brushed every day - we can't possibly do that - wouldn't be fair to our other dogs who don't get it, we just wouldn't have the time"!!!!
Sheryl - if you let us know where you are then someone may be able to recommend a kennel for you to start with
I know of a really good one in Mattersey near Bawtry.