What is a sharp sportsbook
Why do some books' prices count as evidence and others don't?
A sharp book prices to be right. A soft book prices to be attractive. That difference decides whether a price is evidence about the world or a product being sold to you.
Sharp books run thin margins, take large bets, and do not limit winners. They can afford to because they treat informed money as information: a bet against their line tells them something, and they move. Soft books make money assuming the average customer loses, so a consistent winner breaks the model and gets cut.
Why it changes the arithmetic
A fair value is only as good as what anchors it. On the -145 / +125 moneyline the four devig methods span 57.11% to 57.50% — and that is the spread on a sharp price. Anchor the same calculation on a soft book and you are polling the people you intend to beat.
So a soft book contributes very little weight to a fair value here, and is never priced against a consensus it helped set: even a small contribution pulls the number toward that book's own price, shrinking exactly the edge being detected — hardest on the markets where it is the lone outlier and the edge is largest.
Where they never limit winners, no anti-limiting effort is spent at all. Spending edge to hide from a risk desk that does not exist is the most common way that advice is misapplied.