As with all things, one should do some research before making a purchase. As far as AliExpress stuff, I've bought clothing (sizing can be tricky to get right) and carbon stems, handlebars, seatposts, and wheelsets. I generally look at seller reputation and item sold volume and reviews, but it can still be hit or miss.
The most dodgy incident I've encountered was some material flaking off near the steerer bolt area on an integrated stem-bar. I didn't overtighten it; the bolt hole wasn't finished well and a jagged edge caught on the bolt and flaked off. I was ready to trash it but I've also ridden it hard plenty times since then and it's still holding up. I will probably use it on my indoor trainer bike just to be safe.
