When hiring a soccer referee, there is not much to be concerned with but making sure the referee you are considering fits all the basic requirements to handle your game.
The first thing to look for in your potential referee is making sure they are completely familiar with the game. This may sound obvious and basic, but too many times have inexperienced or only partially rule familiar referees taken the field in youth or amateur games. This includes them knowing all the rules of soccer with ease, as well as knowing all associated hand signals that must be given by the referee throughout the game. This seems to be the largest issue and inadequacy of the referees hired for smaller scale games such as youth games.
Next you have the issue of finding a potential and qualified referee. This is usually simple. Usually if a youth or junior soccer league is what needs a referee, the league will manage and find one itself, or seek out a referee that can be potentially hired, which must then be diagnosed to see if all qualifications are met. If you are unable to find a referee in this way, each state has associations containing information regarding referees interested in working in either tournaments or individual games. Upon contacting the association, information can then be retrieved on hiring a referee.
Upon qualifying your referee, you will also want to confirm that they are a proper grade. Grade is a ranking that dictates what types of games can be watched over by certain referees. The grades are given out by FIFA to referees of different experience or training. The grades range from one to nine, nine being the worst. At a minimum for your games, you will most likely be interested in seeking out a grade eight referee. A grade eight referee has attended and completed basic referee training, therefore meaning they are familiar with all soccer rules and hand signals, and are able to ref local soccer games. Depending on how serious the games are you need overseen, you may want to move up to higher grades. Grade seven is simply a more experienced referee, fit to oversee more serious games. Grade six is fit to ref state matches. Grade five is fit to ref national matches, and it gets more serious from there.
It is as simple as finding referees to hire and checking to see if they are adequately knowledgeable or a high enough grade to oversee your game.