Hiya.
I've got the experience you seek. I've sourced on Ali and 1688 extensively, negotiated for dozens of shipments, and had more than a boatload of goodies shipped across the Pacific. I know all about MOQs, PP and TOP samples, etc. When I order I provide my own manufacturing specification sheets, in Chinese (我的中文不錯), so there's absolutely no excuse for any discrepancies.
Oh, and I'm located in Taiwan, just across the pond from Guangzhou.
In other words, if you want this done right, well... here I am.
Zach