We board our 3 1/2 y/o yellow lab about once a year or so. We had no problems until she went home with the wrong family for 3 days while our family went on a cruise a few summers ago. Apparently, there were about 7 yellows at the kennel at the same time and she got put back in the wrong run after her daily exercise with "the general population". The husband came to pick up their dog and obviously wasn't paying attention. The wife came home 3 days later from her business trip (they had no kids) and promptly said, "That's not Molly!".
The kennel owners knew when my wife was going to pick our dog up and had the couple and Molly meet her at the facility. Before they explained it all to my wife she saw them and remarked, "That's looks EXACTLY like my dog". They replied, "We know!" and proceeded to tell my wife what happened. The two dogs were almost identical down to the 2" scar on their inside left, back leg from tumors that had been removed when they were puppies. It's a good thing for them that my wife is pretty easy going. If it had been me, I would have been apoplectic.
In the 30 years this kennel was in business, they said, it had never happened before. Needless to say, we don't board our dog there anymore.
ETA: They usually charge by the pound - We pay $14.00/day. Our dog weighs 85 lbs.