To hire a private investigator for any reason, clients must generally meet with the investigator to discuss the specific job the client would like the investigator to perform, the anticipated cost and other issues, such as the legality and moral issues of the job.
Once a client meets with a private investigator and agrees to the terms of the job, the investigator begins gathering the information the client wants to have. If the job is for the investigator to take pictures of a cheating spouse, he most likely spends a significant amount of time following the suspected spouse either on foot or by car. Following a subject without being seen or loosing sight of the subject is a difficult skill that many private investigators undergo specific training for in order to perform. It involves discretion, subtlety and the patience necessary to follow a subject for long hours without the possibility of a break. The difficulty of the surveillance likely impacts the price of the job.
While investigators are legally allowed to gather information and surveillance photos of subjects, there are some legal restrictions on the lengths to which they may go to gather this information. For example, investigators may not impersonate police officers or use false pretexts to gain access to a subject's telephone or financial records.