When ordering new or used books, CD's, DVD's from one of Amazon.com's small vendors, a customer is offered 3 shipping options: Standard Shipping, Expedited U.S. and International.
In the USPS handbook of regulations, Standard Shipping is flatly defined as Parcel Post rate, nothing else.
Media Mail service is not offered by Amazon, but Media Mail is the service most Amazon small vendors are giving Amazon customers in order to maintain their profit margin. Media Mail service costs less that Parcel Post or 1st Class rate, and takes far longer for the shipment to deliver to its destination than either Parcel Post or 1st Class mail.
For example, a single book sent Parcel Post or 1st Class from NYC to Honolulu will typically reach its destination in 7-10 days, whereas a book sent Media Mail rate will typically take 29 days or more-- a difference of weeks. And shipping Media Mail, the longer transit time (up to 6 weeks, cross country) means greater risk of damage to the shipment with repeated handling and processing, and the routine open inspection of Media Mail, to which Parcel Post and 1st Class are not subject.
The customer pays for Standard Shipping, defined by USPS regulations as Parcel Post service, but the customer gets Media Mail Service.
I phoned Amazon Customer Service, and was told that for a vendor to arbitrarily decide to ship by Media Mail when the customer has paid for Standard Shipping, is flatly against Amazon policy. But every Amazon small vendor I've written to or talked with, says that Amazon actually suggests that sellers ship via Media Mail. They also complain that Amazon has been eating into more and more of the small vendor's profit margin with the fees and commission it extracts, and that it's useless complaining about it to Amazon. So Amazon cheats its small vendors, and these small vendors cheat the customers in turn.
A customer can argue with these small vendors about this issue until they're blue in the face, but most often, you get nowhere. And likewise, you get no help from Amazon, other than a referral to their A-Z Guarantee, which does not cover this issue. Making out an Amazon complaint form is not only time consuming and pointless, as no response or action from Amazon follows it, but Amazon limits customers to submitting 5 complaint forms in their lifetime business relationship with Amazon!!!
The fact remains, that in most media transactions, even though the Amazon customer pays for Standard Shipping (Parcel Post service), they still don't get their merchandise for weeks, because they're getting cheated with Media Mail Service by the small vendors.
I've found it helpful to instead order the media directly through a small vendor Amazon has listed as having the item, without going through Amazon at all, or to contact the small vendor ahead of making the purchase on Amazon and getting a pledge from them to ship 1st Class or Parcel Post for the Standard Shipping fee paid to Amazon, which many have been willing to do.