Edit to previous answer - I think every time you down-vote an answer you lose 2 points. My opinion: that's enough to make sure no one does it out of spite or competition, but not enough to make a huge difference.
Deb is talking about me in her comment, I think.
Because I'm not sure how closely these boards are monitored, any time spam pops up I send a note to Rover. Lately Rover product support has been contributing to our discussion board because they are looking for input on new features, and it seemed like a good opportunity to make sure someone was aware of this proliferation of spam.
I encourage everyone to communicate with Rover any time there is suspicion of illicit activity on this board. Rover is made up of people like us, and they benefit when the company grows. I like to think they value our input.
(At the same time, it is likely that any time an email arrives at Rover from my address, someone in Corporate rolls their eyes and says, "Who wants to take this one from Carmen again!?")
Good question, but I don't know the answer. I sent it via web form to Rover Support. I saw another sitter also identified the problem in her answer to a a question.