Walk away if you must. When in doubt, just don't eat it. Yes, this sucks, but nowhere near as bad as getting sick from the wrong food. This is exactly what I wish I'd done a few months back when eating at a pho restaurant I'd visited—safely and successfully—several times before. The "rice" noodles in the soup, normally transparent, looked suspiciously opaque, indicating that they might have been swapped out for a glutenous variety. I asked the server, then the cook, about the noodles, but our mutual language barrier prevented me from getting a clear answer. I was hungry, in a rush, and had always been fine there before, so I took a chance—and got to be pretty sick for a few days as a result. Fortunately my food allergies are not life-or-death dire, just deeply unpleasant, but still—why eat something that's going to make you sick when there are many, many other things to eat that will not? Sometimes the safest choice is to forgo the food, enjoy the company, and then eat something else afterward.