Coming late to the discussion on the USPS with a few comments. I've had a size business for 20 years selling on eBay and various 'hobby' sites dedicated to cameras, audio, Barbie Dolls, Weddings and others. BTW, if anybody can help me erase my memories of vintage Barbie Dolls, let me know.
1. Free Shipping from Amazon: Amazon has a lot of regional warehouses around the county they stock with commodity items. So the Book/Shoes/electronics you buy from Amazon may be less than 250 miles away. This cuts delivery time and costs. This strategy currently seems feasible for Amazon and...probably no other business.
2. Shipping for Schiit: Schiit is on the West Coast. Shipping a 5 lb Mani can fit into a USPS Flat Rate Priority Mail box and will cost $15 (numbers in this post are ball-park / close but not exact) almost anywhere in the USA. Shipping a 40 lb amp via the US Mail may cost $25 to ship to the West coast, but $125 to ship to the East Coast. This is a factoid that most people who don't ship things simply aren't aware of. Just like most people are totally unaware of greening that can affect vintage Barbie Dolls. (Sorry. The metal ear rings in early Barbie Dolls corroded to a green color, staining the ear and nearby face.)
With such a large price differential for heavier items, calculated shipping as opposed to flat rate makes a lot of sense. Or, you could move the company to the mid-west, equalizing the distance between the East and West Coast and charge everyone the same, adjusted for the company to break even on shipping.
a. When placing on-line orders I also do not like shipping costs sprung at the end of placing an order. To prevent the shipping cost surprise a limited number or rates, or rate ranges, with the cost displayed in a side box might be a solution? Ebay displays a shipping cost if you are logged in most of the time. If the seller offers different rates you can click to see other rates. For Schiit that would likely be too hard to implement.
3. Shipping prices before circa 2003 were pretty stable. Now prices seem to change every few years. Or months. (The change is always up.)
4. USPS has always had the lowest fees charged to the recipient for International Shipping.
5. USPS has favored shipping partners, or something with a similar name. Through one of those partners you can get discounts and the lowest rates, such as First Class Parcel, that you cannot buy directly from the post office. Paypal and Ebay are favored partners, and there are others.
6. Ebay has a severe case of Amazon Envy. They have been pushing sellers to offer free shipping ala Amazon for years. It's a disease.