Ya for instance protein supplements. If you didn’t know you have to be very careful about the origin and the process the company use to produce those. But because it’s very hard to test even with an independent testing company, you have all kind of speculation about which company to avoid and the ones that are good because you can never know. So if you see one company doing shading things or not being 100% transparent then even if the production line is fine it’s still casting enough doubt in the “expert” users to avoid to buy them. And again testing was easy then all this won’t be here. We will just test the protein powder and that’s it.
Mass spectrometry is relatively common nowadays It’s more likely no one wants to pay the hundreds of thousands or millions necessary to do a full test of a single supplement.