HBKSHAWN:
Are you asking about the opening numbers, the ones the books hang up there for a select few to call in and get on them, before they're sent to DB? Or opening numbers as in the lines that are sent to the feed after the loyal sharpies have already gotten down on them?
In MLB, the number is really just what the action reflects. All you need to know is who's booking and who's gambling. You will then find who needs what and you'll be able to make a judgement based on that.
Usually, a number in the middle will not get any business. So if you are standing right in the middle and your books are balanced, you might wanna hang a number in the outside -based on an opinion- in order to get action.
Now, if you're balanced, why go to the outside? That's exactly where the booker with skills shows his game. If you know your players and you know that increasing your exposure on one side will only lead to a specific player to call in, you can then use that extra weight on one side to offer a heterogenous number on the OTHER side; getting more action, but still remaining balanced before the game goes off the board.
There are guys that have an opinion, but they also have the instict and the balls to back up an opinion. Technically, that wouldn't be booking, that's arbitraging. But it works wonders for guys that know what they're doing.
I could tell you who's booking and who's arbitraging -solely my opinion-, but all you need to do is watch the screen, carefully and you'll find on your own. That's all.
Stone Cold:
In MLB, Lenny @ Cascade has built a reputation of being extremely sharp. If you have a screen in front of you, check out Pinny's moves and Cascade's moves. That should tell you a lot.