I'll be watching this thread also. I have bought fabric in the past and am now selling vintage fabrics (or trying to.) I only had one bad experience and it was someone who is in my eBay group. The quality was not the best, though the price wasn't too bad. I just won't buy from her again.
I know one thing hurting me right now is the shipping cost. I even had a buyer ask why my shipping was so high; I responded I did not set the price on USPS. As a sidenote, she did purchase from me.
I also agree you need to check the feedback and ask questions.