from what i know the mark up on the more expensive cloths is much higher than for the lesser ones. i'm referring to what a custom tailor would charge you. for example, if a certain fabric costs him $100/suit, he might charge you $250 for it. if another fabric cost him $250/suit, he might charge you $1000. so if you're going to choose one of his lesser fabrics, go ahead. but if you want some loro piana cashmere, you might be better off first asking him how much he charges for the cutting and construction of the suit, and then trying to find the fabric you want elsewhere. this is assuming you can find it. don't worry about hurting his business. he knows what he's doing when he quotes you a price.