Copy paste from email i got. I assume that they mean only 1 time use coupon per login as the code seems generic. There are many book at $9.99, so if you're interested, nice way to get these for free:
Choose Your Own Free eBook
We now have nearly 700 classic magic PDFs to choose from.
A Free coupon for $10.00 to Spend on Nearly All* Downloadables!
Our summer reading program was a huge success but all summer we chose your books for you. Now you can choose what you want free! We are pleased to give you $10.00 to spend any way you choose on nearly every PDF we offer!
Use Coupon Code: RC10offebooks at checkout**
(*Offer Good for ONE TIME USE ONLY. Any unapplied amount cannot be redeemed later. Offer excludes books by Harry Lorayne, Dani DaOrtiz, Lee Asher, and 13 Steps to Mentalism.)
Ahh, beat me to it! They do have a lot of good classic magic books :)