Don't trade it in if you can help it - those guys are in business, which means they want to make a profit. The best thing you can do is take it to a classical guitar teacher that can evaluate it properly, and ask him if he'll sell it for you on commission - offer 15%. Make sure it's someone that you can trust ,though! That way you'll get the best return for the instrument, and you'll be able to beat down the man in the shop by offering used notes.