Well, I went to a lecture last night with some guys who dove on the Britannic in the Kea strait - 410 feet - these guys were talking about bottles of air (ok, trimix).
The way I figure it, if you got enough brass to get inside that wreck - you can call it bottles all you want - and I might just pick that up...
As far as instructors - just have a chat - it is impossible for a beginner to tell if the person knows what they are talking about - I listened to the language and how comfortable my instructor was talking about anything, I weeded one guy who didn't seem to be able to go throguh a sentence without profanity, not really diving related, but If I don't care for the person, chances are I'm not going to learn much either...
My 2¢ worth.
Terkel