Line shopping
Comparing the same bet across several books and taking the best price — the manual version of what a scanner automates.
Holding accounts at multiple books and always taking the best available number is the single biggest improvement a recreational bettor can make. Cross-book arbitrage is line shopping taken to its conclusion: when the best price for each side, at different books, sums to less than the payout.
Measured on ArbMonster: Compare every book's margin
Related terms: Arbitrage · Vig · Sharp book vs soft book