I have used book buy-back services before for personal "fundraising", but back in February it became apparent that a friend needed help in that area. I sent out emails and FB messages to most people that I know asking them for their used books as a donation to the cause. I received over 300 books, and am still collecting. I have been able to sell back about 25% of what I have received, and the rest will be for sale at a yard sale in May with proceeds still benefitting this friend in need.
I would HIGHLY suggest using book buy-back services! They are a great way to clean out your clutter and you will get more money than at a yard sale. There are about three sites I frequent, but this site will help you determine which site will give you the best price. All sites offer printable, prepaid shipping labels that make it easy to send in the books.