Some very simple advice:
KEH, B&H and others that sell used gear are interested in making a profit. That means they will offer as little as possible in order to maximize their profit. Good business sense, and it will seem generous to the unknowledgable seller who is getting rid of grandpa's gear.
1) Classified ad, either in the newspaper or here
2) Online auction. Set a minimum price, and you're good to go.
3) Private sale.
EBay seems to be the most popular, although with this route, you will pay a listing fee, and if you get paid via PayPal, you'll take another hit.