9/29/2018 update: We only purchased 3rd party used books in 2017 and nothing in 2018. Amazon might well have addressed my problems with their shipping charges by now. )
* Our experience in shopping at Amazon.com (and through Amazon with 3rd party sellers) had been excellent --for over 15 years and through hundreds of purchases. I've not had to return anything sold directly by Amazon and the only two problems (that I can recall) with 3rd parties were quickly and cordially resolved.
* Circa late 2016, however, my frustration level with their obscure shipping costs reached a point at which I thought: "enough!" --after trying to purchase an outdoor television antenna --one which promised free shipping.
Free shipping use to require a $25 purchase --which we easily spent per order. Then it was raised to (just under) $50 --not at all unreasonable.
* Toward the end of 2016 (and I'm vague on the details now), I got the impression (having ended up with a shipping charge --after I'd placed an order) that book totals weren't necessarily added in with other purchases --in order to qualify for free shipping.
So the next time we ordered, I made a screen capture for an item which seemed to indicate "free shipping", but I couldn't get it to come out of the bill by spending more. I also made that purchase anyway, but later on I did a back-and-forth with Amazon's help desk to learn what went wrong. I included the screen shot, but it seemed like I was simply being stone-walled. (Maybe I'd missed something obvious. That happens often enough :-)
* On 2/12/2017, I think I figured it out --at least with respect to my attempted antenna purchase. When the product description stated (something like) "free shipping for qualified orders", the qualification sseemed to be that I should have also signed up for their "Amazon Prime".
To find out what that costs, I ended up having to Google "Amazon Prime". As of March-something, 2017, it meant sending Amazon.com a welfare check for just under $100 --for a year's subscription. (I think that's gone up to $119, as of July, 2018.)
I did not appreciate the lack of transparency and being gamed into that.
* I tried to find out what the shipping on my antenna would be without sending them an annual welfare check but I struck out --short of going through the steps of making my purchase, then backing out near the last step. Although I'd gone through with doing that before, I just grew too crabby and weary of the process --and bought nothing that day.
---Hey, Amazon: just show me the guldarned total cost --with shipping!---
* Through 2017 I returned for book and DVD titles, noticing ever more "free shipping with Prime" flags along the way. Since there was no indication that the old shipping bargain also held (free shipping with whatever total purchase was required), I started buying everything used and from 3rd parties. (Such purchases are charged a constant $3.99 per item for shipping and handling --fair enough, but in 2018 we gave that up as well.)
* My time and equanimity being worth something, I ended up buying our antenna locally. (But first I made one!)^
(Seeing no apparent or convenient way to email/contact
Amazon.com, I'm venting via this web page.)
^The little loop antenna I made
(see: "my homemade antenna") was very helpful
for finding the best location, but I needed a more directional, multi-element
antenna, due to the multi-path TV signals here --and I was able to buy
one locally at a BiMart store.
* As of July, 2018, there are 3 (important to me) items which have become locally unavailable or way overpriced: shirt pocket protectors; thin, transparent, bendable, plastic, 6 inch pocket rulers (a real "vade mecum" for my activities); and Hewlett-Packard, mat finish, inkjet, "Presentation Paper". To my delight, all 3 are available through Walmart.com --AND: shipping is always free if I pick up my order at the local Walmart store.