Ok, am I the only one who pulls a thread about 1/2 inch from the end and cuts along that gap? I was taught that way back in the time machine and I still do it. It is less damaging than tearing. Time consuming yes but then I usually do it while I'm watching TV.
Back on topic though, I would have walked out without my purchase also when the clerk refused to prepare my fabric the way I wanted it. An extra buck on a yard of fabric is too much!(No I don't ask them to pull a thread).