I purchased an 8100 from Amazon last month.. There was no serial number on the box or on the unit but there was on a yellow card inside the box. When i installed Maestro it accepted the serial number just fine. This unit is a gray market version.. The only difference i could tell between the Amazon version and the Crutchfield version is the $700 bucks i saved. The seller at Amazon provided a one year return warranty, no different than $$$Crutchfield.