How Come Used Books Fetch Such High Prices on Amazon?

Having just uploaded Crimson Clouds on Amazon, I keep my book page site under close observation these days, and I noticed something really odd: the printed book version sells for $10.80 and there's a "used" version that sells for...$169.98! See my screenshot (for 25 January):

By the way, that $10.80 is not for the printed version of Crimson Clouds, it's the price for the first edition of the book called A Hook in the Sky and it's not available anymore. I retired it from publication the moment I put up Crimson Clouds on Create Space. I had set up the price at $18 for that printed version, but Amazon has already slashed the price down to $14.99, see here and here's the screenshot:

But wait! The price slashing on Amazon doesn't stop there: within an hour, I noticed yet another change, the price for the printed version had dropped to...$13.18! See the screenshot:

To sum up: you can get a brand new edition of the latest, revised text for some $14 yet some people are willing to pay $170 for the used edition of a previous out-of-print book that was, let's face it, well-received by readers (it got 29 customer reviews on Amazon in its short 18 month life, and over 60 ratings on Goodreads) but it certainly didn't make it in the NYT best selling list!

I clicked on that price to see exactly who was selling and what version of A Hook was being sold at that price - because it has 2 covers, one with the "Hook", i.e. a pile of ladders reaching up to a hook, and one with a naked woman - guess which one is selling for $170...(grin - look at the upper left corner):

No doubt the book cover makes it a juicy collectible. The seller is from Texas and, wow, he's doing well, he's got almost 32,000 ratings and 93% positive. A brisk business! He has a professional-looking "store front", Amazon is good at setting up such pages, look here:

Want to become an "Amazon seller"? The "professional" status which lets you sell more than 40 items will cost you $39.99/month (first month free). Or you go "individual" (for less than 40 items) and have to pay a fee per item sold. See here and here's the landing page:

And here are some links to interesting articles about this little-known world of trade in book "collectibles":

• "How to get the Most Money Selling Your Used Stuff on Amazon", full of tips and read the comments too, very useful:

 from Life Hacker, click here.

• "Can You Make $5,000/Month Selling Books on Amazon?", the experience of one who's been selling books for 2 years:

from B!ZOPY, click here

• "How to make $750 a Month Selling Used Books", another slew of useful tips:

 from the "Penny Hoarder", click here
  
Have you ever tried selling your used books? What is your advice? And if you're an author, have you noticed whether your books were selling in the used book collectible market? I'd love to hear about your experience!