What are the criteria used on dictionaries to decide word classes? 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!
Before 2004, there's no word classes labels in Chinese dictionary. In 2004, 《现代汉语规范词典》add in this label, and in 2005,《现代汉语词典》add in this label.
But it really confused Chinese people because the conception of word classes comes from English, Chinese language do not have a strict gamma system from the start. You can refer to this Zhihu post for more detailed information: Zhihu Post (In Chinese)