Personally, I would choose a employment agency who is strict or even nasty to the maids. They would have gotten the job of making sure the maids stay in line in the first place. SO, solve the headache of being the bad person.
Second, once the maid is in your house, set down rules and personally train her. And don't bother to treat them too well, just make sure that they have enough food and rest. I let my maid eats as much rice as she wants.Sometimes, when we dine out, I will give her good stuff.
And I tell her straight, if you are not happy, you can leave. I can always hire another one. And I always tell her that when I am particularly pissed with her. Never ever let them think you can't do without them. My 1st maid started thinking that way and wanted equality with us (fyi, she had really bad employers before).
So far, I have always given my maids the sack, not the other way around.
Oh, I have a CCTV at home.
Btw, my current maid also says she cannot cook. I teach her and a few times after that, when she says cannot, I told her, can eat cannot cook. She got the message. If she wants to eat better, better learn to cook else we might just tabao while she eats the food she cooks.