Bound Printed Matter and Permits.

With the recent increase in USPS Media Rate, beyond what Amazon allocates for basic shipping to sellers, I've been thinking about switching to Bound Printed Matter, but I don't know if it would work. I am not a large seller. Now, I accidentally used Bound Printed Matter for a book about a month ago, and as far as I know, it got through. I haven't heard from the buyer that it didn't. And yet, when I look up the various regulations for Bound Printed Matter on the USPS Site, there's all this stuff about "permits" and whatever. If I buy my shipping through Amazon, which I do, does Amazon have a permit for Bound Printed Matter? I'd love to use this on a regular basis given the cost difference, but I don't need books getting bounced back to me or unhappy customers. Help...?