Have sold many of my two sons college books on Amazon. But it only makes sense when the going used sales price is $6+ due to the Amazon fees. Otherwise you are screwing around with a sale for very little $. Note that some college text books resale there for under $1 or just a few dollars. Others come out with new editions frequently making older editions depreciate quickly. So in general the faster you turn books around to sell them the better chance u have in making it a realistic and worthwhile transaction.
It's pretty easy to set up a sellers account and all communications takes place via email. Load up on cheap packaging materials and ur set. I always use parcel post, post office media rate. $2.50 - $4.00. I believe they give you $3.99 credit for shipping.
I always price used books near the lowest list price, and usually sell each in less than one week. Naturally, books in good condition usually command some premium.
So "old" books may be better served being donated with u taking a tax write off.