Carmen's advice is great!
There is also a section on Rover where you can add notes to each dog's profile that only you can view. This is how I keep track of dogs that I am not interested in hosting/sitting. In order to make sure that the owner is on the same page and doesn't just keep sending you requests, let them know that you won't be able to work with their dog.
I usually try to format it this way:
- I go over all the fun/awesome things that we did while their owner was away (fetch, pool, dog park, etc.)
- I make mention of any concerning behaviors in a way that is helpful for the owner.
- I point out why I'm not a good fit for their dogs needs.
Ex: "I had so much with (PET'S NAME). As you saw from the picture, they really loved all the sun bathing they were able to get in while we were outside (Point out a fun thing). I did notice, however, that they had a little trouble interacting with some of the other dogs that I was boarding at the same time. (Point out why you don't want to board/sit them anymore). It might be that they just need a little more experience socializing with other dogs (give any helpful advice if you have it). In the mean time, I think it might be easier for (PET'S NAME) if we try to find you a sitter that doesn't have any other dogs present while boarding (shows you want to be a part of the solution, not just drop the client without any help). I'd be happy to help you find someone that might be able to make (PET'S NAME) more comfortable when you travel. Do you want the number for the Rover Match specialists? They can help you narrow down your search to a great sitter!"
Any client that I have turned down with this type of format has been really grateful for the additional help that I've offered to help them find a replacement sitter. This also ensures that they don't keep trying to book you, thinking it was a good match the first time around.