I am a very fussy on-line buyer, but having said that, I buy a lot on line because I'm very busy and it's just easier. I have my two favorite places to go: Connecting Threads and Keepsake Quilting. I use them because I don't have to worry about the quality of the fabric. Even the fabric in the clearance area of both is just awesome. So they're dependable.
I won't buy from Hancock ever again. Worthless stuff. Don't believe their reputation, or fall for their sales. I bought in a "hurry up" sale, and broke my own rules about asking for thread counts and samples. A couple of the fabrics were so thin, I thought they were going to fall apart in the pre-wash water right in the sink. The yellow bled so much, in cold water, that a bright yellow turned into something that only resembles yellow. But I won't natter on here.
I've used several other sites, and before I'll buy, I've written and asked for thread counts of the fabric (if not listed), and often for samples of the fabric, especially if color is critical. If I don't get it, I don't buy. Most of the time, I get what I want. You have to learn to be a little bit demanding with these sites, in a nice way. If you were in a store, it would be nothing to ask about thread counts, or bring in a sample of what you want to match, contrast, etc., so you know you're getting the right color/print. Why expect less of an on-line store? They're still a store, and they should be providing you with proper service. Do this nicely, of course. I can't emphasize that enough. What's that old saying about getting more flies with honey than vinegar? I bend over backwards to be super nice, and then they want to be super nice with me. It works well. Even if they screw up, there is no place for a "bitch" in these transactions. Make them feel it must be your fault somehow, in some way, and then decide if the relationship is worth salvaging, but never burn any bridges.
I have more than one seller on eBay working with me. They know what I like and will e-mail me personally if something comes in. Often they will present me with complimentary fabrics, and always give me the thread counts. They know I like fabric that's at least 200 threads per square inch, or more, and they don't bother me with anything less. I had one seller pull together all of the fabric I needed for a quilt. She did a beautiful job coordinating the colors and prints according to my specifications, and offered up fabrics I wouldn't have thought of, but which worked beautifully together. It helps that she's a quilter too, and has an excellent eye for color. So she saved me a ton of time, gave me more than what I wanted in terms of fabrics that were beautifully coordinated, including the backing, and I got a terrific e-Bay price to boot. How's that for a great deal?!
So take all of the advice you've been given, and give on-line a try, unless you like visiting the quilt shops of course. But once you get on line, you'll be amazed by the variety that's out there.