Sounds great on paper.
It's clearly meant for those who cook. But since you seem to like fast food, let's see...
I wouldn't expect the sales front to know very much, so. A (honest) manager might be a good start, allowing you to compare their notes against whatever other sources you could find, most of which would probably be online. At a nearby cantina I go to, the shift manager actually listed out his three suppliers. Another useful bit of data.
This is the kind of thing I might also try GPT on, which is good for complex searches that pull a bunch of data together as summaries.
But yeah-- get online and see who's complaining about symptoms, and where they likely ate from. See who's done the research and hear where their confidences lie. Build a Venn diagram to help you get a sense for the safest-possible FF places / regionals to eat from. Et cetera...