I think heimish store sales are a totally different issue. A heimish store is claiming it only sells kosher, not that there are kosher components to its items. And if they claim to be only ch”y products, they would need to abide by that as well. People should expect to find only kosher items in those stores unless otherwise specified on the front door somewhere.
however (!) my first time in a “heimish”store (my first time in boro park) I saw a display of granny’s marshmallows back when they weren’t even pretending to be kosher. if I recall, it was a triangle k with gelatin listed in the ingredients. I told the ‘store guy’ that they weren’t kosher and he responded that he got them from the distributor who said they are. I argued with him about it, telling him how I know they are not acceptable and he wouldn’t budge. Since then, I always check labels no matter what joe schmo endorses it verbally.