I haven't done the mage series yet, but someone who has should post reviews. Might help make a sell. Also, I believe Amazon allows authors to post their own synopsis review, don't they?
(Interesting that you only save about 2 bucks buying them used vs. new. Obviously Xaa's books maintain most of their value...)
Edit: Clarification: Obviously Mr. Ferris won't be making any money directly from the sale of used books. What I meant by "make a sell" was that if someone sees the books on Amazon, they may go looking for the first book in the series. And if they BUY those books on Amazon, they will DEFINITELY go looking for the first books in the series!