How do you decline a client after meet and greet?

I just had a meet and greet with a client. She has two dogs, one of them is very nervous. She growled at me briefly a few times through the visit. but the owner says thats just how the dog is and eventually warms up to you. The dog did warm up to me by coming close enough to me to eat a treat out of my hand but then would get really stiff or run away when I would go to pet her. The dog looks like she could lose it at any moment. The dog just seems on edge and I'm afraid that once the owner leaves I'm going to be stuck with a fearful/ nervous and potentially aggressive dog. I want to decline based on just the feeling I get, but I'm not sure how to go about it. I left the meet and greet indicating that I would be in touch with them about getting together again to have our dogs meet up (since she insisted to bring my dog over to play with their dogs when I stay there... I obviously wouldn't want to do this).

Please someone help me by telling me how do you turn down clients after meet and greets when there really isn't anything wrong other than just not being comfortable with their dog... that seems so harsh, and I don't know how to put it. Thanks!