Shipping costs on a return item

[horizon65]

I received a package of stamps that was to weigh 11.5 pounds.  It only weighed less than 2 pounds.  I want to return them for a refund of what was paid and the return shipping cost.  I have also requested this be done before I return the stamps.  He is refusing the return shipping costs and will only refund once they are received back.  Who is right and will Ebay back me up on this?