This is a decent article from Angie’s List. It is important to keep in mind how much the laws vary from state to state regarding construction related work so it is challenging to write a simple advice column about this subject.
As mentioned in the article there are monetary limitations on non contractors in California. I have heard in Florida you pretty much can’t touch electrical or plumbing unless you are licensed in that particular trade.
The key is always going to be a at least a little bit of knowledge/research on the part of the consumer to go with a well recommended provider of services.
Always, only hire someone you are comfortable working with. If the person working on or in your home does not make you feel comfortable they should not be there.