Audio valuations

Is anyone else interested in determining a fair value for used high end equipment? I understand we all try to sell and buy our equipment at the best price, but where to start? I recently listed
a item for sale and set a price that I thought was competitive based on very limited past sale information. I did receive an offer that was $500 less than asking price. Was I too high or was the offer too low. It would be helpful if we could see what others sold their equipment for and the condition of the equipment. I want to sell my equipment, but I don't want to give it away.
Any thoughts on this matter?