there's a website, greenmetropolis.com (or co.uk, not sure which) its specifically set up for selling books, they are all priced at �3.75, 75p of which goes to I think the Woodland Trust, and you get the rest. You register the books you want to sell, then if you get a buyer, the website sends you details of their address and you post the book to them. Have to say I haven't tried it yet, but I have a lot of surplus books and I'm going to give it a go, might be worth you having a look.