I am a Petsitter. After about a year of having an account and messaging potential clients for more information, I finally got someone to reply back.
You can imagine my frustration when I cannot message back to the client's reply. The site requires you to pay for a premium subscription (cheapest is $32usd) to send more than 1 message.
Being a sitter on Petsitter.com is not a sustainable job if 1) The majority of potential clients ghost you, 2) You can't even get a job if you have to pay to get paid, 3) The only way you can make a decent profit is if you overprice your rates, which is just going to drive away clients, resulting in even less jobs.
Long story short, do not look for petsitting/dog walking jobs on Petsitter.com. Use Rover or Wag. Much more people use those services. I do believe they do charge a $15 yearly fee for background checks, however, it is still better than Petsitter.com's ridiculous $106usd yearly subscription.