Zestyut
Google
This is a really intereesting bookshop. It is a bit intimidating when you first go there. For modern first editions, they will only sell the first printing of the first edition, which limits their stock. The stock is very expensive, (if you are a book lover with endless money, this place is a wet dream) but if you are down on your funds, this is a good place to sell to, because they give you around 30% of their selling price so you still get a decent amount. Especially, as selling rare books over the interet is quite difficult.