The same bet is not the same price everywhere
Sportsbooks set their own numbers, so the identical bet can carry different prices and even different point spreads at different books. Line shopping means holding accounts at several books and always placing your bet where the number and the price are best for you.
This is the rare edge available to everyone with zero handicapping skill. You are not predicting anything better than the market — you are simply refusing to accept a worse price when a better one exists a click away.
Small price differences add up
Suppose you want to bet a side that is -110 at Book A and -105 at Book B. Stake $100 at each: at -110 a win returns $100 x (100 / 110) = $90.91 profit; at -105 a win returns $100 x (100 / 105) = $95.24 profit. That is $4.33 more per $100 for the exact same bet, just for shopping.
It also lowers the bar you have to clear. Your break-even win rate at -110 is 52.38%, but at -105 it is only 105 / 205 = 51.22%. Paying less juice means you need to be right less often to profit — an edge you get for free every time.
Shop the number, not just the price
Line shopping is not only about juice. Half a point on a spread or total can flip a result. Getting +3 instead of +2.5 on an underdog means a three-point loss becomes a push (a refund) instead of a loss, and there is no cost to catching the better number if you look before you bet.
Build the habit of checking two or three books for every bet. The best number plus the best price is the whole game — and it is the one edge no book can take away from you.