That's really out of line on the part of the store. Quite rude. You could certainly go into any retail operation and write down the product # mfg retail price etc etc for anything else you wanted to buy.
Also, many fabric stores will cut you little bits or swatches of fabrics if you ask.
Sometimes I think a store might put fabric on a cardboard spine belonging to a different fabric for whatever reason so you should pull out enough to see the markings on the selvedge.
Stand up for yourself!