I think you will get many varied opinions on this. To me, the high quality fabrics are smooth, tightly woven, have some (but not too much) body and drape nicely. Lesser quality fabrics may be very thin (see if you can see the outline of your hand under a single layer), have off grain weaving, have nubs or slubs in the fabric from poor quality threads) or are very stiff from too much sizing used to try to give thin limp fabric more body. If you have a local quilt shop, I suggest you go in and browse and feel those $12 yard fabrics for comparison. Don't judge by price alone however. Also look at and feel fabric from quality manufacturers like Kaufman, Moda etc to start learning the differences. It does take some experience and practice.