when i purchase fabric on line i make sure i am purchasing from a good reputable shop...i've been buying fabric from fabric.com for over 10 years now and have never been disappointed. when considering buying from someplace new i check to see who the manufacturers are ... and only purchase fabrics i know are good quality. if there is no manufacturer information, or i do not know the fabrics i more than likely skip it..
if i really want to try out a new fabric i do not know about i see if they will send swatches...lots of places do, that way i can get small pieces to check out before investing in something i will be unhappy with.