Free credit: Most sportsbooks give you signup bonus/free money. The caveat is that you have to make enough bets to unlock the free money. Hence drawing customers to bet more.
3k wagered: They were betting 3 thousand dollars everyday.
Limited to pennies on the dollar: Most likely a hyperbole. Most sportsbooks will eventually limit your betsizes to say $40 maximum bet on said event.
Did they stop you from betting completely? Introduce a really low dollar limit per bet? Gub your accounts?