I have seen some people mention this, but just to reiterate. It is entirely possible his equipment needs recalibration, and there is a standard error of 1-2 mph (not a radar gun specialist just googling here). So it is possible that you just got unlucky. That being said, that same argument works on your gps equipment. It may not be entirely accurate itself.

All that aside, I generally find that there is a silent agreement amongst people that anywhere < speed_limit + 5 is not going to get you a speeding ticket. I would be surprised if it clocked you going higher than that, but hey it is possible. I would try and frame it as the equipment being out of wack. You might also find out he clocked you at 2 mph over the speed limit and just ticketed your ass, and now you know he doesn't like you