Customer machines are used, but like RD said, flown within all limtations and it is good because you do find squaks that need to be tended to, nothing major just little issues. The aircraft are not abused whatsoever, the instructors know this is someone ship
But rest assured that the helicopters go through a complete five hours of flight testing by flight test. This includes an extensive seven page checklist plus many many thorough inspections before and after the aircraft comes through flight test before it is placed in the delivery center. These things arent put together like tractors on an assembly line, every helicopter is different and everything on the aircraft has certain tolerances that must be met, from how far the fresh air vent knob pulls in and out to the force it takes to pull the mixture out.