What is Rover's protocols if a sitter watched a dog that is obviously neglected by their owner?

Rover has no protocols or role in this. It is merely a platform for sitters and walkers to advertise their services.

You should report to your local ASPCA, Humane Society, or municipal authorities.

I rescue. I also work for Rover. Depending upon degree of neglect and situation, either contact local rescue or local animal control. They both will usually do a welfare check on animals. Weigh in factors such as your area, does AC DO something about these things locally? reputation? are their hands tied in this sitation? legalities? sometimes reputable local rescues can offer better options and help n education to owners.. i would go with Reputable local rescue contact 1st. they will definitely call in the law if it is needed. Pet is priority always! In the grand scheme of things it does not matter who or how - just that they are helped. Do not tink with emotions! that will not help dog and HELPING DOG IS ALL THAT MATTERS! Safety, and. health of dog and you! KARMA IS GOOD - TOO BAD YOU DON'T ALWAYS GET TO WATCH!