Of course, you're right, manufacturers can change the quality from one batch to another, so one kit might not be representative, but if some of us posting here can confirm a specific kit has good components, then it can be a clue.
As I said in my previous post, there are also cloners of cloners, which adds difficulty to the problem...
Anyway, it's interesting to know if the tolerances and precision are good because, as stated here in several posts, there are people willing to spend nearly as much as they spent in the kit to upgrade the resistors and regulator/references. Maybe it's better to spend $2-3 more in the kit rather than spending $10 afterward to improve these components