That's an excellent set of explanations. One way to forestall most of them is the magic phrase "change order".
Anytime you get into a conversation where the customers starts off with "Can't you just..." then it's your responsibility to let them know a change order needs to be filed so you can estimate the new impacts it will have, including cost.
Some of the excellent techniques in OP's article will be employed, but "change order" terminology and workflow minimize these requirements after you've stepped them through the change order workflow once or twice.
Anytime you get into a conversation where the customers starts off with "Can't you just..." then it's your responsibility to let them know a change order needs to be filed so you can estimate the new impacts it will have, including cost.
Some of the excellent techniques in OP's article will be employed, but "change order" terminology and workflow minimize these requirements after you've stepped them through the change order workflow once or twice.