It’s almost as if - by the way you are wording your (very emotive) question - that you don’t actually believe that anyone actually uses baby sitters, that this is all some elaborate hoax. That surely it can’t be true, as anyone doing something so dreadful as using a near stranger to look after their child would be a monster…
They do exist. People use them all the time. They can be neighbours, family friends, childminders, other parents, or people from babysitting apps and such.
From the lack of regular news and media coverage of murderous and abusive baby sitters, I would even go so far as to suggest that it might be even safer than sending your children to (thinking of places that do regularly appear in the news after abuse scandals…) schools, nurseries, clubs, the church, family and friends… and I’d certainly not advocate avoiding sending your children to any of those (well perhaps not the church).
There are risks in everything we do from crossing the road or carrying a child down the stairs, to trusting others with our children. Of course we want to do everything we can to protect them, but we also need to bring up children who aren’t gibbering wreaks who jump at their own shadows, and we, as parents, also need to protect our own wellbeing and sanity and that of our partners.
It is, of course, your choice as to whether you use them. If you are nervous, but want to try, I would suggest asking other parents and the nursery for recommendations as that’s a far better place to start than the internet.
I would also suggest that in future when you raise questions here, and certainly to anyone in person, that you try to limit the judgemental attacks on those that dare think or act differently to you. Difference of opinion and in ways of doing something makes for a wonderfully rich and interesting world and it also is the way that (if we ask, listen and limit our prejudice as much as we can) we can learn and grow and find help.