The only issue I have had is when selling at events or flea markets. If I don't have what they want on hand a few people have been hesitant to pay me for something that will be sent later. What I do is then offer to ship them the shirt (free) and they can then send me the money. Worst case I am out a few bucks. Best case, I get a very happy customer who is more likely to tell others about me. I haven't had any problems with this method yet.