Pet sitting is one of those things that’s usually done pretty informally. You ask your mom, your friend from college, or your friend’s with benefits’ best friend to watch your dog or cat for a couple of days, and you give them a couple of hundred bucks for their service. Unless you’re a professional pet sitter, you’re probably pet sitting both to do a necessary service to a friend and to get a little extra cash on the side. Sometimes people do pet sitting or babysitting pro bono, but that’s usually only if the sitter is a family member who insists on not getting paid. 

There’s a big difference between watching someone’s cat for a couple of days and watching their cat for months on end. If you’re doing the latter, you would probably expect some compensation larger than a couple of hundred dollars. I’m not saying a pet owner should pay the same they’d pay for a kennel, but they need to do something to show their appreciation for the person who’s been caring for their baby for weeks and weeks.