There is a lot of variability in the D800/D800E sensor performance that appears to be a combination of alignment and sensor manufacturing issues. You can test your sensor with reiken focal which will give you a map of all 51 sensor points. I went through 4 bodies before I found one with good sensor performance. What you want is good IQ with minimal change across the sensors.
A quick way to check your fine tuning is to use a tripod and target, focus with live view (AFon only, disable shutter focus) then when in af fine tune, adjust the settings till you get focus confirmation. for the full description of this technique see dot tune. http://www.fredmiran...m/topic/1187638
Usually you have 10 days to evaluate the camera with a refund/exchange possibility.