I often park at Liverpool and have never experienced problems. Just drive straight in, ignore the cowboy sites either side of the road on the way in. At school holiday time the long stay 2 car park - right at the last roundabout just before the terminal building - generally has spaces. None of the car parks ar beyond walking distance of the terminal. Pay at paystation on way out, or book in advance on the liverpool airport website and just stick your credit card in the machine to exit.