# Same side, same market, one moment in time Book A -110 -> 52.4% implied Book B -104 -> 51.0% implied Book C +100 -> 50.0% implied # best line # Taking +100 over -110 saves 2.4 points of probability # on every such bet -- often the entire long-run margin.
Best-line availability differs by market: game lines converge tightly, while props and alt-lines disagree constantly. The practice of hunting the best line is line shopping.
Cross-book aggregation is ParlayAPI's core function: one response carries every book's price for a market from 45+ sportsbooks & sources, and the best-line view surfaces the top of market live. The free tier (1,000 credits/month, no card) is enough to wire it into a product prototype.