As far as your Kashrus is concerned, there is a reason why we have mashgichum and rabbonim there. Their job is to verify that everything is good. If you feel it is not good enough, you should also kill your own chickens and cows, because you are relying on someone else and pesach you should be more machir. You should not buy ANY items from the grocery like potato starch, because you are also relying on other people doing their job.
Whatever helps you sleep at night, buddy 🙂