I've actually gotten some pretty good service from my local JoAnn's, namely in the serger/embroidery machine department. I've asked them questions and they've given me answers that work.
But then, they are there fooling with machines all day long. In general, it's better to ask an older woman in a store like that for help; the young sales people don't often know. Frequently can help you find something if you ask for it by the name on the package, but have no clue how to use it.
I'm trying to remember where it was, but there were channels in the measuring table. You measured the fabric out, stuck your scissors in the channel and cut a perfectly straight line. When I worked in the fabric dept at that store I mentioned, we didn't have grooves, but we did have two pieces of countertop that butted up together a bit unevenly where the end of the yard stick was, so I would use that slightly higher edge to guide my scissors to cut straight. I do wonder why they don't have those cutting tables at JoAnn's and Hanock's. They make sense.