Mandarin is a complete MESS regarding word classes. I can't think of an example right now, but I'm completely sure there are some words that reach the point of being a noun, adjective, verb and adverb depending on how they are used on a sentence.
But sometimes I think Chinese lexicologists and learning books makers just make a random draw of what word class they're going to put there and that's it.
So here's the question: What are the criteria used on dictionaries and learning materials to decide word classes?
Thanks!