A couple of weeks isn't long for a high value item. If they haven't sold it after 2 months, I'd recommend ebay.

I used to sell all sorts of rare books from an ordinary charity shop in Wimborne. eg. A rare Enid Blyton got £15 with no problems. we got about £30 for a Napoleonic war book, etc.

We didn't sell them to dealers, but to ordinary members of the public (who are the people the dealers will eventually sell to)

Half the trick is ensuring they are displayed well, and with card explaining what makes them valuable. eg. Original dust jacket.