Security jobs in your ZIP code
Many small firms might hire a security guard through word-of-mouth recommendation or through someone they know. However it is in your best interests to go through a company. Because in case something happens on your watch, you will not be solely held responsible for it.
Also you will have an accepted set protocol to follow, and you will have the evidence to back up your claim, like logging in regularly and giving the all-clear.
In case you’re working directly and not through an agency, there might not be any back up records, other than what the employer owns, and it will be his word against yours.