I have my autistic teen selling books on half.com. I realize that is an ebay company, but it works better.
You don’t pay a commission until the book is sold.
I’m using this as an educational exercise for this summer and he has made about $43 in three weeks or so.
In actuality though I think the best solution to book is to find a good used book store and get a store credit. You’re likely to get more “value” from doing that than from selling your books because since the economy is so bad, this is one of the markets that is suffering.