In every other service industry tipping is expected for a job well done. I think it would be nice, especially for sitters who go out of their way. Also, If you drop your dog off on Thursday morning and pick up late on Sunday night, for example, the sitter is reimbursed for three nights but really took care of your dog for four days. But if they used the doggie daycare rates they would have been reimbursed for four days. Just something to keep in mind.