I've been quilting for over thirty years, way before they had lqs. In the beginning I would always wash my fabrics, fold them and put them away. When I would finally get around to using them and needed a FULL yard of fabric, I would notice that the fabric would only be about 33-34" long. At first I thought it was because I had washed the fabric. One day I had a pile of fabric from Joanne's that I didn't wash and decided to use it without washing it. My fabrics were only 34.4" to 35" long. I was really upset about it, but there was nothing I could do because I had had it way too long to take it back.
I started watching them quite closely and there were a number of ways they can short you without them realizing it. If I think that their fabric is short I will measure it out right in front of them. This is a subtle way of letting them know that I am watching them. If they make a comment about me measuring the fabric, I tell them the truth, that often times my fabric doesn't measure a full yard when I get it home.
At my Joanne's the clerks hold the fabric firmly when they measure. I asked several different clerks about this and they say that that is the way they are taught to measure fabric. Fabric like polar fleece and stretchy materials I always measure before I leave the counter. This saves me a trip back to the store.