BB compeition questions.

I've never competed nor even attended a BB competition (never really talk about competitions with my bros. who do) but I have few curious questions after seeing the promotion to compete/attend a BB show, the promo had rules and a full itinerary for the contest in the promo/advertisement that showed up in my mail today (prob. had my name sold to them off some supplement company's list). 1. I was looking the mag the which had a promotion/itinerary for a local bodybuilding show. The "show" was for a Sat.: pre-judging then the night show open to audience. The itinerary said Friday night "preliminary weigh in" at 7pm. Then there is the next morning's "weigh in/check in" at 8am-9am. (Followed by pre-judging (noon) then the evening show). Why the two weigh ins? And which of the 2 "weigh ins" determines what weight class you compete in? 2. Same local show required "proof of age of less than 20 years of age for teen class" and proof of age for "masters class". How complicated is the proof of age typically/on average are we talking a drivers license only and/or maybe some form of simple 2nd I.D.? I hear about twenty something year old dudes in the "teen" class using fake I.D.'s so they can stomp on the real teenagers competing. How prevelent do you contest in-the-know guys think this is appox.? (Reminds me of pro baseball players never being the age they say they are). 3. The Olympia states it specifically tests for diuretics. Does the Big O test for steriods at all (I am of the understaing that they don't and it is diuretics only)? Or could a competitor take AS, GH, and basically whatever works for him, except diuretics right into the to pre-judging and into the night show? Are the diuretic testings random or mandatory for all? Thanks bros.