Argee with Umesh, educate people at point of sale. Some people are going to buy a diesel car despite a petrol making more sense, they get blinded but the MPG figures and the £30 or £105 a year road tax. Either when you are quailifing these people or at point of hand over a basic outline of how a DPF works is a must. Simply telling them that the car needs to be driven at speed for 5-10 miles a months to allow the filter to clear itself out is all it takes.
Then its upto them if they follow your advice or not.