What kind of old gear? Transistor receivers from the '70's & '80's won't be worth much, other than a few classic models. Same for most turntables [Duals's & Garrad's]. With speakers, many of the woofers used a foam surround that decomposes to dust over the years.
If you want to tell us what you are planning on selling, we might be able to tell you if you got a "winner" or an eBay special.
The Orion Bluebook & Agon's own Bluebook are more of an approximation than a hard and fast firm price.