I think you just need to set up a space in your house where you would keep the bunnies and Guinea pigs and take pictures of it for advertising your business. You could make flyers to post at local vets and pet stores. I even saw someone with one of those magnetic signs on their car advertising a pet sitting business. There's always Craig's list for advertising too. It would probably be a good idea to have references available from friends, other people you have pet sat for, and/or your vet.