Think of this as a job interview, and you are the employer, and are looking at potential candidates. If someone passes your initial phone screen, bring them in for a full interview.
You should come up with a list of expectations for this job, and interview candidates in your home when your children are around to get a feel how they are going to work with your children.
Look at things like:
- How do they interact with your children, are they excited or is this just "a job".
- Can they change diapers/make bottles/make meals/etc.
- Do you ever see them take out their phone during this time when things settle down..
You can get a pretty good impression of someone in a short amount of time.
If and when you do hire someone, I would definitely suggest cameras, and let them know they are in use as that will bring about some sort of accountability on their part.