Hashgachot

Question

I appreciate your answer regarding hashgachot. I have showed it to mant people. But my original question still remains. There is a home made ice cream store near my house owned by a non-obsevant Jew. She assures me that all the ingredients are kosher. Can one rely on this or, since she herself if not Orthodox, one needs a hashgachah as a guarantee. Unlike a bagel store, I assume that there are a variety of non-kosher ingredients that could be added to the ice cream, if the owner wished. Thanks.