Are they both saying they come with the same fabric, nailhead and pillows as shown? Also, perhaps one has spring-down cushions and blend-down backs but the lesser expensive doesn't. Couldn't hurt to call the two sellers as well to get more info.

If you're going to spend over $3,000 on any sofa, you should purchase it from a brick and mortar store, or a very reliable online vendor (Pottery Barn, Williams Sonoma, Ethan Allen, etc.), where you can touch it to feel the fabric, and sit in it to see how comfortable it is.

Those 2 sofas do look exactly alike, and have no descriptions attached. I'd be very wary of this vendor.