it's like with speed limits.

quality or safety testing in any industry is done on a sample - you can't test everything.

There are regulatory bodies and testing labs. Even in Mexico or if anyone ever found out they would be unable to export, costing them $$$$.

You either trust in the way these regulations work, just as you trust that every other business does not screw you over, although they only get inspected/QC periodically (filthy restaurant kitchens, faulty carbon frames, ...) or you don't and buy regular (which is subject to some restrictions too).

yes, it's true that you can still use certain sprays or other stuff on organic products. copper on wine, for example.