First of all, hoping that the cop doesn't show up for court will be in vain...All officers are "required" to show up for court or they will be disciplined with days off without pay.
Second, the officer does NOT have to show the radar to someone if they request to see it. It is the officer's discretion whether or not they wish to allow the violator to view the radar.
Third, every officer is required to check the calibration on the radar unit before they start using the unit and after they stop using the unit. They will usually document this on their copy of the citation that goes to the court. Today's modern radar equipment is very accurate. I've used the Stalker radar units when I rode motors, and they do not put out any kind of a radar signal until I pull the trigger. I get an instant reading, pull the trigger again, and I've got you. I have even stood in front of vehicles with radar detectors, hit the trigger waited a second and hit the trigger again, and the person's radar detector did not go off....WHY? The Stalker radar sends out a signal ever 1/1000 of a second...the average radar detector is capable of getting a radar signal ever 1/100 of a second...You do the math!
Just pay this ticket, remember that it's not wise to pass an officer who is working radar at a speed over the posted speed limit....If you want to contest the ticket, at least take your car to a reputable place to have the calibration on the speedo checked. Then you can attest that the 75 setting on your cruise was correct. But then again, if you admit to doing 75 in a 70, technically you have admitted to a speeding violation! It isn't whether or not you were actually speeding, it's how much you were speeding!
One more thing....you said that you had set your cruise "just before you passed him"...the Stalker radar that I mentioned earlier has an effective range of one (1) mile! So it IS possible that you were going faster than the 75 before you set your cruise control and he nabbed you before you ever did that.