I'm not sure that the drive is more complicated, but it's a mechanical part and it could have been damaged in transit. They are nowhere near the level of returns that Sinclair had with the spectrum in the 80's.
commodore shipped known bad computers to meet demand, knowing that instead of buying a competitors product that was in stock the customer would have a broken computer under the Christmas tree. They hoped that they'd have manufactured enough working ones before people demanded a refund.
I worked in a small repair shop in that time frame. There were curious things in customer units that we repaired, but all that was confirmed later. In the summer of '85 we had trouble getting parts to keep up with a nasty lightning storm season so we bought several brand new C-64s off the shelf to cannibalize. We had to laugh when we found the boards were all very obviously refurbished and slapped in new cases.