I was hesitant to put my recent experience on this topic because it is not going to help the running discussion. Now I'm on vacation and (mobile) Internet has reached even this remote tropical paradise, I thought of jotting it down.
Yes, the customers have high demands in all fronts, performance, availability, security, ... - all at the same time! During the initial discussion, once they hear about the various levels one could have in each of these fronts, things get even worse. Then in the middle part of the discussion I start to quantify those demands to realize that there are no hard figures. Rarely I hear, "we need a four lane bridge, spanning 200 m between point X and Y, which could carry 40 T trucks on two lanes, which must stand a 50 y flood, ..." rather, "the voters said yes to a bridge across ..., it passed the council..."
Anyway, to make a long story short, rather than offering the biggest solution which the customer can afford, I finally offer them a whole series, from basic to maximum, with clear specs and costs, and most importantly, an upgrade path once the need arises.
And my experience is that a surprisingly big proportion of them stay with the (modest) plan they've started with. Though less attractive financially these are success stories for me from an engineering point of view. Also, I hope, that way I've contributed less to an ever accelerating environment disaster.