Antique lady's desk/piano desk

I have this antique desk that was left to my father by my grandmother when she passed away.  We know that she originally paid $1200 for it, but we have no idea about the actual value of the item.  We took it to a local antique dealer who offered us $600 for it, but her actions and refusal to look us in the eye or answer any questions led us to believe she was making us a very lowball offer. 

We are not experts on antiques and want to make sure that we have a solid idea of it's value.  I've attached several pictures.  Any help would be greatly appreciated!!  I do have several other pictures I can post as well.