When I first started working at a LQS (don't work there now) I was the only one who liked country quilts. Everyone else liked bright, bold, loud quilts. In good fun we’d laugh and joke with each other about our different tastes. They’d yawn at my quilts and I’d put my sunglasses on to look at theirs. Then I converted to a bright, bold quilter but still like quieter ones too. They also came to appreciate country and plaid quilts.
It takes time for a quilter to learn and grow. Tastes change. I believe if they like what they have done and are happy with their quilt that is all that matters. If they are pointing out a flaw and specifically asking for help to improve or stop a mistake from happening again then giving them guidance tactfully is good.