Well, not sure it warrants being p.o.'ed, but, you have to consider that owners that ask that question (and you're right, many do) have probably owned it for a long time and it's become almost like a family member. In other words, the vehicle itself means a lot to them. Has nothing to do with your plans for it after you buy it in reality - but they may indeed not sell it if you tell them you're gonna lower it and chop the bed, etc - or they may at least not lower the price when the haggling starts. So, really, the best answer is probably - "I'm just gonna enjoy it, it's a great old truck - thanks for taking such good care of it all these years" if you're seriously wanting to buy it. No need to tell them that your definition of "enjoy" involves a sawzall.
Even if it is sacrilege.
