Are you in a large city or near one? Most record dealers will give you pennies on the dollar for used vinyl even if there are some records within that collection that are worth far more. The alternative is to find a local collector who is willing to go through the collection and give you some sense of value. The only way to maximize that is to retail the records, which is time consuming and labor intensive. I got rid of quite a bit of vinyl that was 2nd, 3rd and 4th tier in terms of value (both to me and in the market) by working with a fellow who took the records, handled the ebay listings, fulfilled the orders and remitted a % to me. Saved me a lot of trouble.
You could go to a site like Discogs or Popsike and get a sense of value, but it is going to be very time consuming if you don’t know how to quickly cull through a collection. Many dealers will use those sites to price their records-- sometimes, in my estimation, over true market, but it’s at least a data point.
Very few hi-fi dealers are interested in used gear unless it is vintage collectible or hi value. That is the reason this place, Audigon, ostensibly exists- for people to unload their used or unloved gear and turn it into cash. I think there is a blue book value facility on this site but never used it. You could, conceivably, research each piece of gear and get a range of asking prices from Internet listings. (I think gear that is sold or for which listings expire here doesn’t show the prices and those were ’asks’ anyway).
FWIW, unless it is a real high value record, most classical records these days bring very little money b/c the market for them is small.