For those publishing paperbacks through KDP Print, you'll know there's an option to enable 'Expanded Distribution'
It pays 40% royalty instead of 60%, but I normally enable it because I'm keen on the idea of people being able to order my paperbacks elsewhere (other retailers, bricks and mortar stores, etc.)
However, here's why it's bad. For this example, we're using a short paperback of around 180 pages.
Let's say you list the book at $9.95 retail, with around $3 profit. On the expanded distribution line you can see there's an 80c royalty (approx.)
Your product page goes up, and the first thing you see is that the cheapest copy available is $9, from a third-party seller. Oh well, you think. At least it's a sale if someone orders from that guy instead of me. (There are usually half a dozen third-party sellers on each paperback product page.)
Well yes, but that guy pays amazon the expanded distribution price, you get 80c instead of $3, and 'that guy' most likely charges an extra buck or two on postage to increase their cut.
I don't sell many copies expanded distribution. The figures come in once a month, on the 15th or so, but today it was 18 copies. Almost all were for my kids books, and that's cost me US$40. Not a hell of a lot in the scheme of things, but look at it another way: Third party sellers took 80% of my royalties for those books, for zero amount of work. (Everything they do is automated. They don't see the books, they're shipped direct to the buyer.)
So, I'm going through and turning off expanded distribution on ALL my titles. As a bonus it means I can lower the prices a little as well.
I've been setting up hardbacks through Lulu recently, as well as paperbacks with global distribution. (I can't be bothered messing around with IS/LS again so I'm not looking for recommendations on other printers, as I'll rarely sell anything outside KDP print anyway.)