I'm surprised you sold your Rolls Royce so cheaply, the profits from camera sales must have bbeen high
Joking apart the margins on new camera sales plummeted in the 70's & 80's and never returned to the 100% mark up level, but the OP is talking about selling second hand items to a dealer. That dealer has to finance his stock and unsold goods cost money in interest etc, some dealers as well have better infrastructure and reputation (and are much larger) and can turn items over faster.
In the UK it's better to sell as a commission sale through na dealer, that way the tax (VAT 20%) is on the commission only so far better for the buyer, it's better for the dealer as well because they've not had to pay before the items sold. The down side as a seller is you only get paid when the items sold but then you get a far better price. That's been my experience anyway.
It is supply and demand, I was amazed today when doing a Google search to see how many UK shops just sold analog cameras & film, many successfully. But I know one who's prices in his shop & on Ebay are way too high, but friends who jo him says he's been paying far too much for stock.
All shops /dealers have to make a living. the moral is sell to one who's turning over stock and check ot the best options, in the past for me it's been commission sales when through a store.
Ian