Contact them and find out!
I've rarely had issues where I needed to return online fabric purchases, but when I have contacted the companies with issues they've always fixed it right away. I think online companies are very aware of forums like this and they know we will talk if they don't treat us right!
I think I've only returned fabric to Fabric.com, once, about 2 years ago. Actually I didn't even "return" it as they told me to just keep it and sent a refund. (It was fabric that bled and faded really badly with just one wash - I emailed photos as proof. They didn't want it back.)
A lot of online shops will send swatches for free or for a nominal charge as well.