I think these two quotes are a great summary of some common problems.
Half the time an announcement is made, there's a storm over common or departmental radios of people picking apart every tiny little detail, to try to unravel the legitimacy of said announcement without ever giving it a chance to progress. Leeway has to be given on both sides. Should you be expected to act like a total idiot to give every possible chance to antags who don't even try to be believable (as arrow said)? No, of course not. On the other side, should you expect the antag's announcement and story to be 100% watertight, with no flaws? Also no. That's just not going to happen. Leeway is the name of the game here. Command, maybe allow them to walk around while you fax central instead of keeping them cooped up (Or maybe don't fax central. Heresy). Antags, maybe don't load up on totally obvious weapons and gear if you're going to pose as an inspector or liaison. There needs to be concessions from both sides, as well as minimum standards of reasonable and realistic action. It's a balance.
(At the same time, I understand why antags WANT to load up on all that stuff. 1) It's cool and 2) There's always that worry that security is going to shut you down and arm up, or ERT is going to come and erase you. But trust has to start somewhere.)
But as people have stated, this doesn't seem like a cut and dry thing to be able to enforce. I think this is a discussion the community needs to have, but as an official policy with actual enforcement? I don't think there's much we can change here. Arrow's point about interaction generation is a good one. I don't feel that there's a good way to implement this policy without it feeling kinda forced.