Sharp action is typically when a player makes a bet and then the line moves in his favor. Not once or twice. Think dozens and dozens of repeat times.
For instance, if you grabbed Denver right after the Championship games, and got them at +2, that would be 'sharp action' as the line is now -2.
Does that mean Denver will cover tomorrow? No.
Sharp action wins and loses, just like coins go on heads or tails.
Books are known to cut off and not take action from people winning.
Casinos are known to kick out ppl counting cards. This isn't like banning the 400lb guy who comes into the Golden Corral you own and kills food costs. That is a lawsuit. Shops, for the most part, can do what they want.