Most of the charges people call hidden are ordinary costs of flying. They arrive late when a quote leaves them out, marks them “if applicable” or bills them “at cost” after the flight, so a short quote is not always a cheap one. A broker's own fee is usually built into the total rather than shown as a line.
Read every quote for the items below, and ask for the answer in writing: included, estimated, or billed later.
De-icing
Billed by the handler on the day, because it depends on the weather. Winter departures from the Alps, Scandinavia and the northern US need it most, and a delay can mean doing it twice.
Get in writing: whether it is in the price or billed afterwards at cost.
Handling and FBO fees
Each airport's handling agent or FBO charges for the aircraft and its passengers, and some US FBOs add a facility fee unless fuel is bought there.
Get in writing: handling at both ends and at any fuel stop, in the total.
Landing and parking
Landing fees by aircraft weight, parking for every night the aircraft waits, and slot or permission fees at busy airports.
Get in writing: parking for each night of the trip, and any slot fee.
Crew overnight
Hotel, transport and a daily allowance (per diem) for the crew on every night away from base, and on the longest legs a second crew.
Get in writing: crew costs for every night away, and whether a second crew is needed.
Positioning legs
The empty flight to collect you and, on a one-way trip, the flight home. A quote can show only the hours you are on board.
Get in writing: both positioning legs, shown in hours or as a figure.
Fuel surcharge
Fuel is usually inside the hourly rate, but some contracts let the operator add a surcharge if the fuel price rises before the flight.
Get in writing: whether the price is fixed once the contract is signed.
Catering
Drinks and light catering are usually included; meals ordered for the flight are often billed on top.
Get in writing: what the standard catering covers and how anything ordered is charged.
Wi-Fi
Not every aircraft has it, some systems only work over land, and data can be billed by use or by the hour.
Get in writing: whether it works on your route, and how it is charged.
Taxes
In the US, Federal Excise Tax applies to domestic charter flights. In the UK, Air Passenger Duty applies to most departures and VAT to some routes. Elsewhere it depends on the country and the routing.
Get in writing: which taxes apply to your routing, and that each is in the total.
With every line answered, quotes from different brokers can be compared on the same basis. The private jet quote comparison worksheet lists each line to check.