Basics: if you are hiring someone with a credential of some sort, like a CNA or NAC, verify it and any sanctions on your state's online database [free]. Google everyone and almost invariably if they have a criminal record of any significance, it will come up, but you can also pay to search specific databases. Finally, trust your own instincts while interviewing. We have all walked the other way to avoid someone on a dark street. Your brain is geared to protect you. Once you have someone good, ask them for referrals/passing the word if you need more people.
Of course, campus job databases are always a good place to start and are often free, as well as your own networks from friends, family, work, community, church, library, senior center, etc.