My last speeding ticket was the same..clocked by the cop oncoming. The cop claimed I was going over 70mph. I had purchased the car the day before and had been advised to keep under 60mph for the first 500 miles so I knew I was not going that fast. I had specifically driven to the rural area around my old hometown for slower speed rural roads. Typical cop radar is not accurate for oncoming clocking due to what is called cosign error... the angle at which the radar is measuring from two oncoming vehicles constantly changes. Some states do not allow radar speed measurements when the cop and target are both moving. I went to court and had my case dismissed when the cop did not show up to testify.
That's not true. If it was true once that was a long time ago. Any radar nowadays will calculate the aspect ratio and correct for both that and the speed of the patrol car if it's moving. Once the aspect ratio gets too high the relative motion will be too small so you'll fall into the doppler "notch" and won't be able to get a speed reading, but as long as you get the reading it'll be accurate. Any radar today is going to measure your speed a lot more accurately than your speedometer.