Let's say you have a dish in front of you but you're not certain what its ingredients are. You ask a Gentile who is familiar, and he says, "I've seen something like this before and it's usually made from X (which requires bracha A). But your dish looks a bit different and it might be made from Y (which requires bracha B). So, I'm not 100% sure."
Even after tasting it, the Gentile isn't sure. You have no way of finding out otherwise what the food really is. The Gentile knows nothing about brachot. If you ask another Jew, he would know less about it, and would probably shrug his shoulders and say, "make shehakol".
An example of the above - you order a Chinese dish, and it is some type of dim sum (dumplings). The inner ingredient, which is the majority, has chunks and you have no idea what it is. The Chinese Gentile says, "it could be made either from wheat gluten (mezonot) or taro (adamah). I don't recognize what you have, it's probably taro."
For purposes of this question, you don't have access to eat other "definite" foods of either category to cover both doubts.
Can you rely on the Gentile's opinion that since it's most likely X, and you should say bracha A. Or, because he's not 100% sure, and you know a lot less than he, you should just say shehakol in all cases of doubt?