Great idea...easy for the HVAC company to understand and test. Our system was replaced last year and as part of the sales process, we were asked if there was any hot or cold zones in the house. The master bedroom and bath were always either too hot or cold because the duct work had to be routed around basement stairs. All those bends caused the air flow to be cut way down. The salesman came up with a rather elaborate "solution" but the install team merely changed some jumper settings on the new blower moter to increase the speed which in turn increased the amount of air entering the master suite...problem solved in about 15 seconds. Just a thought you might want to remember when you get ready to negotiate and various options are discussed. Good luck.

The only way to truly effectively damper a forced air system is with dampers where the individual runs meet the plenum or main branch, NOT at the end of the run in the room.