Investigations can be expensive, so you before beginning an working with a private detective, it is important for both client and investigator to sign a contract outlining what is expected in terms of deliverables and reports, and what the fees will be to attain those deliverables. Many investigators require an up front retainer fee, plus additional fees for expenses such as fuel, photocopying, photo processing, meals, parking, etc.
Do not hire an investigator who will not agree to produce a complete and verifiable accounting of his or her expenses on a weekly or monthly basis unless you are prepared for a potentially unpleasant surprise when you see the bill. It is easy to ‘pad’ expenses, so if there are limits you want to impose, do so at the beginning of your negotiation, so that both parties are aware of any financial restrictions. Having all of this information in writing will protect you against any unscrupulous spending a dishonest investigator may try to incur.