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Don’t spend your money unless you seek a career in test flying, and anyway you could pick up the basics for that from the manufacturer’s test pilots over several acceptance flights.
A reputable manufacturer will not put an aircraft up for acceptance that is not ready and any ‘testing’ that you undertake is most unlikely to detect anything untoward with the design. Therefore just go and enjoy the flights.
Take as much time as the manufacturer will allow and take the opportunity to learn about the aircraft. From your current experience on type you will naturally detect any significant differences or quirks in a new aircraft. The majority of the airline’s acceptance is conducted by engineering and the cabin staff; these are aspects where the manufacture may have less experience than an operator. Always take an engineer with you, preferably one who has flown before else he will snag every new noise. Take a working cabin crew, not management (they forget the practical past too quickly). Evaluate the aircraft as though it were in service; try all systems, switches, knobs, galley, seats, doors, toilet etc at high cabin diff.
Use your time with the manufacturer’s test pilot to enhance your experience. Stall the aircraft in straight and turning flight, and in several configurations. Conduct harsh maneuvering by rolling and pulling to give you a better feel for the aircraft – and compare how it may differ from the simulator (if different its the simulator that is wrong). Similarly fly over-speed IAS and Mach as allowed; experience the Mach buffet or turn buffet points if applicable. Shut down and relight the engines; add to your experience of asymmetric flight and ask for a demonstration of Vmca. Do those things that you would not normally do with passengers, but may have to in an emergency e.g. GPWS pull up, baulked landing go-around, TCAS / wind shear pull up. Fly emergency configurations as allowed, hydraulics failed, control malfunctions.
Brief the cabin crews that the flight is also part of improving their experience; and don’t forget the brown bag for the engineer.
Aircraft fly by the same principles on an acceptance flight as at other times; the only idiots in flight are those who don’t ask questions. Test flying is fun; have fun.