People tend to bash China made product on every forum. Often they do it on their Apple computer or Apple phone that is made in China..... Go figure....
Anyway, in my own manufacturing experience, China makes some outstanding stuff, some mediocre stuff, and everything in between. Its more about what the customer wants, rather than China making crappy stuff.
BTW, in the world of cheap manufacturing, China is no longer "cheap". Check out various well known branded bikes that are now made in Cambodia.
On seat posts, I keep a box full. Some 26.6 posts will measure close to 26.6, others will be closer to 26.4, even though they are marked 26.6.
The Stein tool above is a good one.
I tend to run a brake hone into the seat tube, particularly if the existing seat post has zigzag marks on it. I don't get carried away with the home, its just knocking down any high spots inside the tube.