I've gotten a few of the $5 credits for various mystery authors, or even specific mystery books in some cases, presumably because I read a lot more mysteries than romances. However they've usually been on books that are in the $9 - $11 dollar range before the discount, so even with the coupon, they're usually not at a price I'm willing to pay.
I sort of think this may be a more targeted continuation of the old Random House (or was it Harper Collins?) $5 offer, which gave $5 off almost any Random House book regularly $9.99 and up. But the programming didn't seem to take into account if the book was on sale or not - it went by the regular price. So a few times I got lucky, and a book or two that I wanted went on sale during the validity period of the discount, and I was able to pick up some books for free. There's a thread somewhere on MR about those credits. They were very confusing to try to use...and even more confusing when I try to write it down
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