Who made the gun? For an good condition original M
orporation M10 that's a great price in either 45 acp or 9mm. For RPB or RPB/MAC is a good price. For a Cobray is ok. There are others made by Jersey Arms or other companies, but they don't seem to hold the value that well.
Stay away from the ones that use plastic mags. The mags wear out quickly and the supply is getting worst.
Don't worry too much about how the exterior looks, just make sure the interinal is in good shape. Some sear has been worn out so badly that the gun won't stop until the mag is empty - every dangerous condition! Replacement parts are still easily available.
If the dealer has a matching-serial-number suppressor, buy it by any means - it's the most valuable (aka expensive) combination of any MAC's.
Be prepare to buy ammos in bulk
Personally I have a RBP M11 in 380, and I rarely shoot it for both value and finacial reasons
It has the fastest rate of any model. I got the brief case and suppressor for the gun, too. I always draw a crowd of people at the range everytime I shoot it from inside
the brief case.
Many modifications can be done to make them shoot "accurately", but who cares when it's time to "rock'n roll"!!!