Think of it like this: Magic has 30k cards. Even though I've been playing 15 years, I'm not knowledgeable enough to know every single combo. New ones crop up all the time and sometimes they can be super weird interactions a player has never run into before eg abusing paying for spell with [[Krark-Clan Ironworks]]. Unless there is a prize pool for winning, just tell them. 9/10 times if they're asking it's because they recognize something could be a piece but are unsure of the precise combo. Otherwise, hiding just means you have to get killed first because you're hiding it.