Agree! I only go to 專門店 to buy things. You spend a bit more and have the guarantee of real ones. If you buy from somewhere else, you'll never know whether those are "A"or "B" 貨 and you carry it around. How awful! My opinion is that either save more money to buy from 專門店 or buy no brand name ones.
Milan station, they buy your bag or not is depends on the style, if your style is out-dated, they will not buy as no one will buy. Also, if your bag look old, they will not buy it also because the margin is low compared with those looked new.