Am I right in saying that an expert is someone that has the mental tools to solve certain problems whereas someone who's not an expert doesn't have those tools. For example, a plumber knows how to work with pipes so, if you don't, then you should listen to them when it comes to pipes. And this would only work with objective matters, there can't be an expert in something subjective or normative because there's no way of knowing what's true or false or when the "problem" is solved.