I have many textbooks that I’ve only used a few times. I’d like to sell them all at once to like a bookstore or what not and get a lump some for them. Do you know of any websites or stores?

I’m in university and I am debating on whether I should sell my used textbooks or not. Obviously, I could potentially earn back a good amount of the money that I spent buying the book.

But still, is it worth it to sell? And, should I sell it personally (as in person-to-person) or sell it to the campus used bookstore? The Used Bookstore provides an official receipt but only offers 80% of the profit to the seller. If I sell it person-to-person, I figured I could sell it for at least 90% of its original price but no receipts =(

Which brings me to my next point, how do you determine the price of the used textbook? I know that you can’t sell it for more than the price you bought it for… but what is usually the percentage of the price that students sell them at? 90%? Will someone buy it that high? I mean, I just want a good fair amount of price on my used textbook if I’m going to sell them.
Pls. help… I’ve never done this before…