Here is the way I tell people to approach sales in my shop.
If you don't like the price I offer, you don't have to sell to me. Period, no hard feelings, there you go.
Until you hand me your cards, and I hand you the cash, we are still negotiating, and you have the right to say "no".
When you go to a dealer to sell your cards, expect not to get full e-bay values on them.
50% is a number commonly used, but sometimes higher is paid, and sometimes lower is paid.
When you go in, have an idea what you want to receive, what you are willing to accept, and be ready to walk away if need be.
What I am TIRED of hearing is people saying "the vendor ripped me off". No, the vendor did not rip you off, you ripped you off. You accepted the offer.
Now, the complaint, "The vendor only offered me XXX, he was trying to rip me off", is at least a little more valid, until you accept the offer.
If you think you can get more scratch for the cardboard, go get it.
If not....accept the offer.
My 2 cents.
Vince