Sharp books take large bets and set efficient, low-vig lines; soft books cater to recreational bettors and move slower. Sharp lines define the fair price — soft books are where +EV value appears.
Sharp books (like Pinnacle, plus exchanges like Betfair and Smarkets) welcome big bettors, have low vig, and adjust instantly to sharp money. Their prices are the most accurate — which is why a consensus of sharp books is the best fair-line benchmark.
Soft books (most US retail apps) cater to casual bettors, carry more vig, and are slower to move their lines. That lag is exactly where +EV opportunities and arbs show up — a soft book price that hasn't caught up to where the sharp market has moved.
Use sharp books to estimate the true price, then bet the value at soft books before they adjust. The trade-off: soft books limit winning accounts, so bettors spread action and shop widely.
Pinnacle is the classic sharp book, along with exchanges like Betfair, Smarkets and Matchbook. They set the reference line the rest of the market follows.
Because they profit from recreational action, not from sharp bettors. Consistently beating them gets your stakes cut or your account restricted.