Do your homework.
If your first time shopping with a brand is at a sample sale, you better do your homework. Don't shop blindly by picking up your usual size because they vary for each brand. A Steven Alan shirt is cut differently than a Thom Browne oxford, so size accordingly. If you're unfamiliar with a brand's fit, check for measurements online, call the stores and ask, talk to your friends that own a few pieces, or just go to the store and try things on. Trying clothes on at the sale itself should be your last resort. The time you spend playing dress up is better spent shopping.