Seems it's easier to tell customers that their wants are mis-informed and technically not feasible than to just go ahead and deliver what the customer wants!
I second your response - the most difficult thing about ignorance is that we may be too ignorant to recognize it! Or - if we say "I don't know", we fear the weenie meter!

If we're not sure about something, yet continue to present ourselves as though we are, the discourse becomes pontification (what the heck does that mean?:).

I have found that in situations I have little to no useful knowledge on "the" topic, that the prospects seem to appreciate a simple "I don't know.". It is also a useful phrase/gambit when one of the prospect's sidekicks is trying to argue the virtues of a particular point on which he is (obviously) ignorant.

The rules are simple - keep foot out of mouth!:-)