QA can be a big differentiator between competing companies that share upstream suppliers. It could be that one sunscreen maker is testing for crap/contaminated precursors and another isn't.
Good point. The difference between quality products sometimes just comes down to specified mechanical tolerances and purity levels of chemicals/ingredients. Though price usually increases much faster than quality at higher levels. Going from 95% to 97% pure might cost $X, but 97% to 99% will be $X * 5.
