They are notoriously hard to capture in photos, unless you do extreme closeups. Even in show venues, where spotlights are directly on the quilts and have beautiful sparkle in person, that sparkle rarely shows up in photos unless you take extreme closeups as illustrated in this blog. And even then you are really seeing the crystal in the photo not the sparkle.
http://www.quiltingjewel.com/2011/04...-crystals.html
Quite honestly, if you do manage to capture the crystals in a photo it probably won't make the "but it, don't buy it" decision for a potential customer. They will buy based on the overall appearance of the wallhanging and I doubt the bling of the crystals will be the decision maker for your potential customer. But the closeup shots would be nice. Hopefully you can post multiple pics. If not, then I would opt for a photo that captures the whole quilt and talk about the crystals in your description.