Traci
I've run a small rural boarding kennel for over 30 years and maintained the same policy (it also gives me a chance to start up a conversation and get people thinking and learning!).
I require a healthy, parasite-free dog or cat coming through the front gate or they are turned away. No vaccines required! I also inform each new client of the policy and if they aren't comfortable they are free to book elsewhere. I've never had anything more than an undetected flea or tick here and there :-)