In other words, you could be paying top dollar for an investigative agency's name, but the work is being performed by a trainee who hopes to be a real Private Investigator one day. Fees are not regulated, so it's best to check with a couple of companies. Normally, Private Investigators require a retainer for their services. Generally, you are billed for any expenses incurred during the course of the investigation. For example, some Private Detectives charge fifty cents for every mile driven, while others include mileage in their hourly fee.
Some Investigators have a mimimum fee for each surveillance operation.
If the Private Investigator's minimum fee is 4 hours, this means that if they only work for one hour, you still pay for four hours of service for that particular day. This is done in the movies a lot, but in real life, it's not likely to happen. If an Investigator is willing to agree with these terms, they are generally inexperienced or in desperate need of money. Neither scenario is good. Payment in advance is a customary request among Private Investigators.