I had one get past me, back before reverse search was as easy as it is now. It was the Vineyard Vines whale, customer brings it in on a printout because email was harder then and smartphones weren't around. Didn't know it until my wife(then girlfriend) saw the screens and pointed out what it was.
Oops.
I had someone wanting the dragon from Pete's dragon on some shirts, and I passed on it. Disney probably wouldn't be happy if they found that online(which is where he was selling them)