Hi @largo ! Welcome to the forum! How wonderful that you’ve had such good experiences with your sitters!
To answer your questions. A sitter will save your listing if they like it but are unable to do your posted dates. When you list new dates, they will be automatically notified. A sitter is not notified if you save her/him to your favorites.
Note: you can click on the spyglass icon on the upper right and enter a question or search terms as many things have been discussed in the past. There is a ton of useful information there!