Charter, also called air taxi or ad-hoc flights require certification from the associated country's regulating body such as the FAA in the U.S. The regulations are differentiated from typical commercial/passenger service by offering a non-scheduled service. In the U.S. these flights are regulated under FAA Part 135[1]. There are some cases where a charter operator can sell scheduled flights, but only in limited quantities[2].
Lastly, don't be afraid to ask about safety: Any reputable operator should have safety information prominently featured on their website, and won't mind answering questions about their pilots, such as how many hours they have flown. (At least 250 hours, which is what it takes to get a commercial license; NetJets mandates at least 2,500 hours; Wheels Up, mandates 7,000 hours for a captain and 4,000 for a first officer.) Gollan suggests fliers ask if the pilot has any health issues, and feel free to ask if the operator (or plane itself) have any accidents or incidents in its history. is an extension of Sentient Jet Charter, LLC (“Skyjet”).  Skyjet arranges flights on behalf of clients with FAR Part 135 air carriers that exercise full operational control of charter flights at all times. Flights will be operated by FAR Part 135 air carriers that have been certified to provide service for Skyjet and that meet all FAA safety standards and additional safety standards established by Skyjet. Skyjet is a registered trademark of Sentient Jet Charter, LLC, dba Skyjet.
On 1 April 2017, there were 22,368 business jets in the worldwide fleet, of which 11.2% were for sale.[5] 5-year old aircraft residual value level is at a 56% of the list price.[6] A new business aircraft depreciate by 50% in five years before depreciation flattens between years 10 and 15, and the owner of a 15 to 20 years old is often the last, matching luxury cars.[7]