Problem with the price differentiation is that you will find de higher priced cars (and mostly more serious maintained cars) at the Porsche dealers and specialists while a lot of the cheaper cars can be found a the local car dealer as stated above. These local car dealers can't do anysthing serious with the cars since they have no customer relations interested in Porsche so the only option is to sell the car for a low market price. And since there are many of those cars for sale prices of these will drop dramatically. Ofcourse all cars also a 996 will drop in price, its just a car, but those dealers dont know what to do with it. A friend of me is buying exclusive cars from those local dealers for low prices and sells them for market conform pricing, so far he does a good job over the last 15 years
As soepkip already stated it can be pretty interesting to buy such a car as long as you are aware of the risks and history.