Many private investigators require an initial deposit, commonly referred to as a “retainer,” before they will agree to accept a case. This retainer may be established based on the predicted amount of time that the private investigator will likely be required to expend. Other investigators may base their retainer fee off of the service that is being requested of them. For example, computer research may require a much smaller retainer than cases that will likely require much surveillance, such as an adultery case. Once the private investigator commences work on the project, he or she will deduct the fees as they are incurred from the original retainer.