I have bought fabric on ebay with no problems, but agree you really need to read the description carefully.
I like to buy fabric on etsy.com. I have had nothing but great experiences. (NOTE THE S on the end). I have bought quite a few things. Several times I want a group of fabrics that go together and they will put together sets and email me picturee and let me pick out the fabric and then make a private listing for me. It's not a bidding process, but you still can get some really good deals. I bought some Red Rooster fabric the other day for $3.99 a yard. Pretty good considering the new stuff coming into shops is nearing $10 a yard. It is a really great place to look when you are looking for a specific fabric. It is also a good place to sell your finished items. I have a friend who sells quilts on there.