Well, I spoke with Amazon. For the first 10 minutes the nice women attempted to ensure me that there was no way Amazon opened the product and it was definitely new or as received from the manufacturer. (Is it possible the Pentax checked them before sending them to retailers?)
Eventually, she agreed to speak to a supervisor and returned a few minutes later to let me know that they would be overnighting me another Pentax which would 'most definitely be new'. I have 30 days to return the original order... I do have to pay return shipping but they will reimburse me upon receipt of the camera.
I'm certainly satisfied with that, but I'm hoping I'm not returning a camera someone 'checked' for one that was not checked....
It seems far more likely that the one I received today had been returned by someone earlier... I guess...