Dealers will only offer you a 1/3 or 1/2 the value they have to make a profit, taking into account time, effort, storage, that's why they're called dealers. Your living in a dream world if you think you will get the SO called book price. Who decided that the book price is gospel anyway.
I could have sold my rarer, popular records 100 times over but then your stuck with all the others to drag out everywhere hopefully selling them, quite often taking them back home, same again the next week, then there's eBay, PayPal charges, postal charge etc, etc. 99 % of people selling up are making a massive profit on what they paid so why not accept the dealers offer, you will still be quids in.
Steve