I can't tell you how hard it is to have customers taking pictures of your designs and telling the people they are with that the item isn't worth what I priced it at. Wait till they try making it themselves....I am able to buy larger quantities of things, like seam binding...so able to keep the price lower. A package of 3 yards is $4.
As you know, it takes time to work out a new design...and it isn't fair to have it copied at the next craft show.
I have a sign posted in my craft booth, too...."Please, NO photos allowed".