I have purchased fabric from Walmart. I used to go there to purchase fabric when I was going to make a quilt for someone that I suspect would not care for it and appreciate all the work that is put into it.
I got a good tip from our quilting guild the other day. If you hold the fabric up to the light and put your hand behind it, you should NOT see your hand or outline of it. That is a sign that you have quality fabric. Try it, it works!