You’re almost there - “fit like” is an expression particularly unique to the north east of Scotland, and it’s super versatile. On it’s own, it’ll mean “what’s happening” or “how’s it going?” - then it can be used in various contexts like “fit like i day” as in “how are you today?”, or in this case “you ken fit like”, “you know how it is” or “you know the score”.

“Maybes naw” is pretty much spot on though, unless used in the context “maybes aye, maybes naw” where it’s less of an unsure expression, and more of a deliberate evasion of the question.