I've been trying to sell the MAC-10 for sometime now and have had absolutely no luck. One out of state NFA dealer was going to charge me the $400 transfer fee for gun and suppressor that I was trying to sell. Two Oregon dealers never bothered to respond to my inquiry one way or another and a third after initial contact and email has failed to return communication.
I thought buying the MAC was difficult. As it turns out I can't even sell it at a price (which when compared to other similar packages) is basically a steal. I was given the impression that the MAC-10 was an investment sure to increase in value. What I have is an expensive toy that I don't shoot and can't sell.
Mac did some work for me sometime back on a little Colt .380 which I have since sold, (I sure wish I hadn't).
There is a great article about Mac in the September/October 2010 edition of AMERICAN HANDGUNNER.