I'm going to make a wild guess and say that that maybe you are younger or more tech savvy than that sales clerk was/is.
I was teaching a lady English and using a book that she wanted the information about (name, publisher, etc.). She took out her phone and took a picture instead of writing down all the info. I was startled, but, after a second, realized that it was the easiest and fastest way to keep that information.
I don't think that they should object. I can see if people abuse it, but I think in the end, good customer relations should win out. I may not buy my fabric there (in this case), but maybe I'll come back and buy a ruler, or check out the sales, etc.