No, you don’t. The exchange is to take care of houses and pets as if they were yours in return for staying there for free. Sitters pay for their trip and food. Some things can sometimes vary, like food or fuel if they lend you their car. I have also heard about home owners who ask sitters for apying pay for power and water expenses during the stay, but this never happened to me. In any case, they should let the sitter know in advance. And, of course, any veterinary expenditures are at the expense of the owner.