(Picture by Roberto Casati, Paris Orly Airport, August 2013)
“Save time and use your credit card to pay at the car park exit”
Hidden premises are risky. You may hide only as much, and if you are caught in the act, blame on you. Your entire communication strategy collapses. Honesty is not a decoration in communication.
In parking lots at Paris airports, you are billed by the hour. Each our started is due. At 4 euros to the hour, it makes a difference for you if you stay 58 minutes or 62; each of those extra minutes costs you two euros. We all used to pay before entering the parking lot and collecting our car. Now we are asked to pay at the exit gate. Suppose it took you ten minutes to get from the automated cashiers to the gate, there is a chance in six that you are one of those customers who will pay an extra hour.
The communication strategy is that you will end up saving time. But time, in this context, is money that you do not save. Why not tell, instead, that it is preferable not to have people for too long in the parking lot after they have payed?