1. Do not give away your eBay ID to anyone at the store.
I overheard a man telling someone else in the store his eBay user ID. I always see this guy on half price days buying up dozens of shirts, ties and blazers. Of course I was curious and checked his profile when I got home. I knew most of the brand names he had listed, but I did learn of a few new names and now he has someone else to compete with.
2. Do not act like you are buying items to resell.
I had a man online today as I was checking out tell me that the brand I was purchasing was really good. I actually had 2 items from the brand. So I just told him oh yeah they look nice so I was buying 1 for me and 1 for my wife. If I was to tell him yeah they are great sellers on eBay. What is to stop this guying from looking for this item to resell? So just becareful what you say.
I am not saying what brand I am talking about right now because it is my #1 seller and it will be in my first eBook: My Top Ten Thrift Store Items to Resell on eBay. It will be ready next week at a low price and it will pay for itself with your first sale of an item in the eBook.