Hidden (?) units.

[cjsiam]

It is important to clarify misunderstandings of the rules before play commences...
And there are occasions where two intelligent humans can both make what appear to be valid
interpretations of the rules---or they might seem to be on first blush.

I see no problem with an ongoing effort to seek a universal understanding of the Rules between players.
On occasion, when agreement/consensus can't be achieved--a die in the game, and then review of future gaming opportunities would be appropriate.

Blatant misplaying of clearly laid out rules needs to be challenged, and honestly stopped, else bad habits develop when 
such a player is confronted with the actual rules....

Rules Lawyers have a role in assuring that the interpretation of the rules is true to the best translation of the Authors intent.
Optional Rules, and modification are all valid too--if players agree...
Personally, Peter's mods, including Double-blind make the best games I've seen...
But, that's just me.