As an employer, you have to put a certain amount of trust in to your employees. This may be to allow them to communicate with your clients, correctly quote for work or to handle sensitive data. When you are looking to recruit a new member of staff, it can be hard to know who you can trust as often you will not know any of the candidates that have applied for the job vacancy.
Firstly, have a good look through their CV. See if there are any gaps in employment and ask them about it during an interview. You could also contact some of their previous employers for a reference as then you will get a true picture of how they work.
Some people lie on a CV stating that thy have skills or experience that they do not, one way to check this is to devise a little test or project for them to complete during the interview and see how they get on.