I can only speak for Dassault Falcon - they have their own team of pilots that ferry aircraft from France to KLIT for completion. Typically woners/flight depratments then do acceptance flights looking for need to fix items - these flights are flown with Dassault pilots. Afterwards the aircraft are usually flown home with new owners.

On occasion the manufactures advertise for pilots for demonstration/flight test. These pilots do everything that I mentioned previously to include fliying the aircraft for potential buyers.