As in the secret service, the best individuals are intelligent, articulate and proactive professionals educated, clean-cut; they are trained to prevent threats to your wellbeing.
Compare these specialists with two hundred kilos stereotypical thugs working for Britney Spears or Madonna. These “bodyguard” can only react to a threat and usually work as porters or bounty hunters and “supplement their income” as a bodyguard and often lack the specialized training.
Search internet about legislation for private security companies in your state and the license required for “bodyguard” or “Personal Protection Officer” or something very similar. Candidates need this license to work for you. Having said that, do not assume that a license of “bodyguards” of any state is in itself a good indicator of their abilities.
Most states have no requirements for a license to carry weapons, a few have very strict training requirements and others have a shockingly low training requirements, which do not meet any recognized minimum standard of training. These licenses have names like “Personal Protection Officer” (PPO) or “Personal Protection Specialist” (PPS) and usually are required for the individual to work for you, but most are acquired with very little training, as anyone can get a license of “Security guard” or pay $100 for a course of “Bodyguard”.
If a candidate attended a school that is not in the list, make sure the instructors openly identified, have extensive experience (over ten years) in Government Protection Services, or a civilian equivalent, and if the course has minimal of 100 hours for formal training of security staff.