Out of print - I would not do half.com.
Ebay, maybe - but books are difficult. I have a 100 year old set of 22 volumes of Voltaire's collected works. they retail for over 1000 euro if you have a buyer - I have never found a buyer.
With no UPC I can't list them on half.com, and with Ebay I am stuck with a one week listing and an extravagant listing fee if I try to have a minimum bid as well as little chance of selling.
Try to find a real book seller and negotiate a deal - there is really nothing on the net that will guarantee sellers decent money.