I'm just curious.  :)  It seems to me like it might take the price of purchasing a book brand new, then subtract shipping (or cost of a credit)...  and perhaps also subtract some extra for mileage and time?  What do you think?  Does anyone know for sure?  :)

If you hover your mouse over the "money saved" in your account, you'll see that they base this on a used book price of $4.50.  I think this is a lowball estimate, so you've probably saved much more in reality.

Oh cool!  Never occured to me to hover LOL.  Is this is a hobby of yours, mouse hovering??  (Had to say that with your little cat icon LOL!) 

It's just the number of books you've received x $4.50, though.

So despite what it says, it's assuming you've saved $4.50 per book, which means you have to subtract out the postage you've spent to get those credits. So it implies the price of a used book is some number higher than $4.50.

I realize I'm just nitpicking.

MMP: $7.99 - $2.13 (postage) = $5.86. Trade Paperback: $12.00 - $2.13 = $9.87. Used MMP $4.00 - $2.13 = $1.87. Used Trade Paperback: $6.00 - $2.13 = $3.87. Even if I only bought credits here @ $3.25 each, I am still saving money on all but the Used MMP, and considering they come right to my door with my books, and I dont have to tote books anywhere to hope they will take them for a trade, PBS is the best bargain for me.