Yeah, parking lots are usually private property, and unless the police dept. has written authorization to make misdemeanor arrests there, they don't. They can write you for reckless driving though. Besides, who would be setting up radar in a parking lot? No other way to know they were doing 90 mph without it. Also, going 90 mph, you would be across most parking lots in about two and a half seconds? Maybe they were just blowing smoke rings.