Unfortunately (and, of course, from my personal experience), vast majority of photographers are too vain - they rather want to hear false praises than honest and constructive criticism.
However, I don't (and I never-ever wouldn't) lie them in order to get a few extra bucks, so the honesty
and constructive criticism
are always a way to go.
In other words, my motto is:
"Give a man a fish, feed him for a day. Teach a man to fish, feed him for a lifetime."
And if somebody doesn't want to learn to fish... well, their stomach will growl, not mine!