I used it several times with my old dog, not because I needed it, but because I'd thought it would be nice for my dog (who was highly social) to make new friends.
I've only met very nice people on it, always met them beforehands, never had an issue with anyone.
One of his regular borrower was taking him to her office once a week, one day I was walking him and 4 people came to us to say hi, they were the borrower's colleagues and absolutely loved my dog, that was so nice.
He was a very easy dog, super comfortable with everyone, just a happy little chap really, I left him with a lot of friends who were always happy to be looking after him.
My now dog, I wouldn't leave them with borrowers, just because he's way more high maintenance, so I prefer to pay. But I still quite often leave him with dogsitters that I've met on rover, and likewise, never had an issue. I set some rules (only one dog - mine - at a time, never leave him alone, no off leash walk etc...)
I've been using dogsitters / dogwalkers for 20 odd years, and up until recently, it was not a regulated trade in my country (not sure it actually is now), you just have to meet people and trust them at some point. I must be a good judge of character because really, I never had a problem.
On the other hand I would never leave my dog in a kennel or take him to doggy day care, all of my dogs would have hated it.