Ask them for the start up/commissioning report that they are suppose to do for your system. Things like the static pressure, temperature rise across the HX ( Heat Exchanger ) gas pressure check at manifold, field ( sub-cooling, superheat ) refrigerant charge is to manufacturer spec.
To keep them somewhat honest. Certainly they can fudge the numbers thou...
Make sure system gets registered ( California or Quebec does not need to be registered to receive the manufacturer maximum parts, HX warranty ) as your manufacturer warranty will be decreased if not registered.