Best way to turn down a client that is doing multiple meet and greets?

I had a meet and greet yesterday with a family with 3 dogs and a cat. Although a friendly breed, 2 female dogs are "head shy" and take time to let you interact with them. This family is interviewing several Rover Sitters. I have thought about it and prefer NOT to take on this client. Do I let them know immediately or should I just wait for them to choose in the next 48 hours. My concern is how it will affect my record on Rover as I am brand new. Is it better for me to reject now or wait and if they don't choose me, I don't have to explain why I do not want to pet sit for them.