PARKING FINES : SO MANY  COULD BE AVOIDED IF PRIVATE PARKING COMPANIES ACTED IN A DECENT HONEST AND RESPONSIBLE WAY 

Decent honest private car parking companies operate a sensible, fair and just system to the benefit of all motorists. There is an entry barrier by which a ticket is acquired to gain access. No need of any requirement to enter vehicle plate registration details.  There is no looking around for an available parking bay because when the car park is full the entry barrier cannot be activated.
Moreover , the motorist does not have to predict what number of hours he needs to purchase. Predictions are real profit generators for the company : either they are over generous which inevitable leads to overpayment , or they are under-estimates leading to overstays and nasty savage PCNs. Motorists are therefore on a hiding to nothing. 
In respectable car parks , the motorist only has to pay for the actual time of his/her stay , by entering his ticket on his/her return into a machine which then calculates the tariff, takes the money and validates the ticket to activate the exit barrier. Beautiful , fair and involving no loss to both parties.
Why this barrier system is not adopted by the parking pirates is obvious. The potential loss of revenue from saving the motorist from over-payments, overstays and miskeying in car registration details is huge. This customer-focussed system does not generate sufficient profits. Motorists are error prone and this human condition needs to be exploited , Forcing them into into making bad or wild predictions , and careless mistakes when keying in car registratiuon details ,  is a what their evil business model is all about.
Ticket systems need to be simple and fair , having the customers' interests in mind.  They should not be designed to exploit the motorist out of their unsatiable greed for profit. Rogue parking firms are nothing more than vindictive , ruthless, money-grabbing bastards , which I hope and pray will be brought to task when new parking law legislation comes into force.
In the meantime , my advice is to overpay rather than overstay. Take great care when keying in those seven characters. Challenge each and every PCN where injustice can be established, and if feel you were in the wrong..... only pay a reasonable sum , which clearly equates to the actual loss the company could legitimately claim.