the key is preparation not only in materials to backup your claim and questioning to challenge MPAC's finding (e.g. gathering sales data and value for comparable properties in your neighborhood, you can get most of these from MPAC site) bcz MPAC rep there has done this many many times and has a long "working" relationship with the board.
also note, you can ask for info (arguments) MPAC will use at hearing, that should be part of your preparation for the challenge obviously.
good luck! MPAC has had problem for years and well publicized. they had a such bad reputation that they were pretty much "shut down" (halt) for a couple of years.
