Be thankful that you don't live in a country where the police can and do fine on the spot for whatever offence they dream up. It all bolsters the treasury kitty or their own pockets if you don't think to ask for a receipt.
Here in Germany, as well as neighbouring Luxembourg, France and Belgium we have on the spot fines. Speeding fines are always on the spot, unless you are over double the limit, then it's court. Been done a couple of times and all fair and square - never any trumped up charges. In fact, as you must always carry all documents on you, once these are inspected, I have never known a cop to look around the car. Trucks, they do sometimes. They always issue receipts, and having no cash is no excuse for not paying - they carry a mobile credit card machine in the car.
That said, a friend was done in belgium (on a German registered car) a couple of years ago and heard over the police radio a notification from one cop to another that there was a Porsche heading his way doing 155 kmh (limit 120). Asked what plates it was wearing and when told it was belgian, was told to leave him.
So in this area it's not so much a case of trumped up charges - more a case of cops favouring their own nationals. Difficult in Luxembourg - only 49% of residents are nationals.