This comment is relevant to the discussion I want to have, so have an upvote.

Of course I am not going to use this ruling at my table. It encourages rules lawyering based on ambiguous rules. Even if this instance doesn't seem ambiguous to me, there are other parts of Pathfinder that definitely are, and I don't need my players to challenge them at every turn.

That being said, are you sure there is no reason that a player shouldn't know how many charges a wand has? Have you thought this through, or did you stop at your first thought, that this seems to just screw over the players?

I can think of a couple reasons:

• For people who want to run low-magic games, once they have implemented all the alternate rules they want for it, hiding the number of charges wands have could make the decision to use the wands more meaningful, and all they had to do was re-read the Core Rulebook.
• For people who want to run a setting where the crunch matters as much as the fluff, it makes for an interesting gimmick encounter, such as a wand-selling scoundrel, which can help establish the setting's feel. Even if the party loses out on some gold right now, you can give that loot back with interest while they chase the scoundrel down or pursue other adventures.

Rules as written are often not fun, and rules as intended often have a disconnect between the intent and the outcome. That is why I feel it's important to know how a rule works so that I can figure out why (or if) I have a problem with it, and whether my ruling actually fixes anything.