I wonder if the sender is also an Amazon seller?  I used to do both, but rarely sell anything on Amazon anymore. 

Or, maybe the sender's copy of the book you requested from him or her was nonpostable after all, so they just decided to order a copy for you through Amazon???

MaryF

Books sellers are not prohibited from membership, so could very well have been from a vendor.

Yep, there have been a number of members commenting in threads lately-- but they are not "businesses", just individuals who try to sell books on Amazon or Ebay.  I don't mess with that, just use Amazon or ESCO book buy-back programs at end of year and see what I can get.  If it's next to nothing, I will post a textbook here, but only if I need credits-- not worth it to ship a really heavy textbook .

It could also have been a copy someone ordered from Amazon, then repackaged in the same wrapper when it was time to mail it out to PBS.  As long as I get the book I'm promised in postable condition, I could care less who it's from.