Trade in value to a dealer

I have some items I would like to liquidate and reinvest the proceeds into upgraded equipment.  I have no feedback on Audiogon and wouldn't enjoy selling if I did.  I am interested in experiences you have had with trade in value to a dealer.  Let's say I have an amplifier which I would normally sell for $3,000 and a set speakers which would sell for $1,500 if I were to sell them to an individual.  What expectation might one have if trading these items in on more expensive pieces? 

I have no experience in this area, but in comparing it to the automotive market, I would be getting a wholesale trade in value.  Do most audio dealers operate on the same basis, wherein they feel they must make a profit on the inventory they receive via trade in, or might they allow a fair market value if they are making a profit on the item I am buying from them?  I am sure it varies from dealer to dealer, but am interested in other's experiences.  Should I expect to take a big hit?  Or maybe just a slight cuff?  Thanks.