I have bought from fabric shops at $10/yd and it's frayed away. I've bought Walmart and it's lasted nicely. I feel fabric, look at the salvage or bolt end information.
I was told at a retreat with a factory rep there, that the huge roll of fabric, cuts off into bolts, the end is flat folds (our Ben Franklin store), and it's sold the same everywhere..fabric stores only buy 1-2 bolts so price is higher, Walmart buys thousands of bolts so price is kept down. JoAnns & Hancock don't buy as much as Walmart, but Walmart is also closing fabric dept. We have 12 stores in the state and only 2 have fabric now..prices might go up.
There are a higher quality of fabric you can watch for, where designers require better thread count, better dye, better processing. And other's that are mill basics. Do a hand scrunch test at the store, feel the fabric, nothing you can 'see' through. But before it was mentioned, they don't take time or energy to separate fabric to Walmart or a Quilt shop, it's all off the same huge fabric roll. And I've paid high price too often at fabric shops for crappy fabric..it's not the end all perfect buy, but I do like to support fabric shops..usually more selections, they offer classes, more tools than you can find at Walmart or JoAnns or Hobby Lobby...just point out to your fabric shop owner if you find crappy fabric (discretly), and that you'd appreciate the better grade like Moda, etc. Hancock you can return cut fabric now, I will, if it frays, has flaws. Wish all stores would offer that.