This site has one of the clearest views of the fabric - it shows the swatch with a coin, the fabric draped over a stool, an extreme closeup revealing the weave. It has some of the best prices for silks and cotton/silk voile. Their ordinary price is about 30% off but they often have 50% to 70% off - then I stock up.
The problem for me is that I tend to overbuy on the cheap fabrics because, well, they're cheap and so am I. They often have good deals on designer fabric, but they also have a lot of furniture fabric and some sleazier stuff. The pictures combined with the descriptions are pretty thorough.
I've never returned anything, but I've never needed to. I've been ordering a few times a year for several years now.
I assume the customer service is good, but I've never had any cause to test it. Shipping has always been fast and correct.