I have a variety of fabrics in my stash. You will be able to tell bad quality. Just because something comes from a box store does not automatically make it bad. If it feels flimsy - it won't handle properly or hold up, but even a flimsy piece among mostly strong blocks will be absorbed - particularly if it is the perfect pattern/color.
Don't buy $2 fabric if it is poor quality but don't think you need to buy only $10 yardage only. There are a lot of choices in-between.
Happy shopping!