Once you've sold something, I don't believe it is yours anymore - is it? Lets say for the sake of argument that the OPs Ritchey really is worth $1,500 to some collector because it is serial
#1 . If the purchaser figures that out because a) you don't know, b) you don't have the time or energy to clean it up and describe it as such, or c) the purchaser has access to buyers you don't who expect him to find valuable things; then is any of the profit owed to you? I know where I stand on that argument.
This is why we have markets. And freedom. Be happy we don't live in a country where you have to acquire permission to sell things, or pay bribes to locals to open a stand at a market.