I’m very sorry that you’ve had this experience, so remarks just made to help to get a more consistent good match with sitters. I only petsit through THS at the moment, but I have pets and a home and have done a lot of homeswapping during decades on another platform.
I wonder what happened when you’ve had several bad matches. How is your screening process? Is the listing and the responsibilities there described so that the right sitters apply for the sit? I will for instance not apply for more complicated plant tasks, as I know I am not able to keep “plants with specific needs” alive. Are your applicants experienced sitters with good reviews? Do you have good video-calls or similar where you discuss the pets and expectations? Do you have low applications so that you tend to accept sitters that are not what you would ideally prefer?
Can you do something to make the success rate better? In listing, screening - or as suggested - take down the tasks a notch by for instance having a drip-system for your plants so that even someone like me 
would dare to apply and be able to keep your plants alive?
I’m really just trying to help you. If you want, you can also start your own topic in the welcome-category and add the link to your listing in your forum profile, if you think it could be useful to get some input.