Even the best investigators come up empty on occasion. If an investigator guarentees results, be wary. You should provide the PI with clear instructions on what you wish to accomplish. You should be kept informed on a regular basis as to the status of the investigation. Any work necessary that is in addition to the original request must be approved by you.
Most investigators require a substantial retainer up front.
Ensure that you understand the fee and expense structure. In addition, mileage and actual expenses are also charged. If you have any questions with regards to hiring an investigator, or have hired an investigator in the past and were unhappy with the service provided, send me an email. I will answer all inquires regardless of your location.