I found this twitter account of a guy who says is a oddsmaker for a south America company.
It has some interesting info. Aparently, If you are have a "winner" acount in a bookie, is easier for you to move the line.
I selected just a few interesting tweets to share.
#2 ( this one could be an explanation for this: http://arbusers.com/index.php/topic,1690.0.html )
Make bookmakers cash cow machines