I'm watching the WB show Gilmore Girls right now (hey, don't laugh - it's a well-written show). Rory tells a teacher that she bought the teacher's book new, not used, so the teacher would get full royalties. The teacher responds, "I get full royalties whether you buy the book new or used." Rory quips that she's learning something already.
But what she's learning isn't true. Authors do not get "full royalties" on used books. In fact, authors get NO royalties on used books.
No royalties at all.
Just so we're clear on that.