#1373 2000 · Betfair · Gambling / online marketplaces
Betfair replaced the bookmaker with a matching engine and took 5% instead of 25
问题
Bookmakers baked an average 25.6% margin into the odds; bettors could back an outcome but never lay one
背景
Sports betting ran through bookmakers who set odds with a built-in margin — the overround, the sum of implied probabilities minus one, averaged 25.63 percent across a 700-race academic sample. Every bettor paid it on every race, and could only ever bet that something would happen, never that it would not: taking the other side was the bookmaker's monopoly.
In 2000, Betfair launched a person-to-person betting exchange: a matching engine pairs those who want to back a horse with those who want to lay it, at odds they negotiate on screen. The exchange does not price risk — it matches it, charging commission normally capped at 5 percent of winnings, and the bettors themselves quote the prices, so the book shrinks toward the commission.
换别人会怎么做
Become a sharper bookmaker with lower margins — still inheriting inventory risk and the cost of pricing every market yourself, while the exchange's customers did the pricing for free.
他们看到了什么
The bookmaker's 25% margin paid for pricing risk he never wanted to hold. Let bettors lay as well as back and they price each other — the exchange just matches, charges 5% of winnings, and carries no risk.
那一手
Letting customers take both sides turns betting into a continuous prediction market. Traders quote prices, arbitrage the exchange against the bookmakers, and trade in-play — backing at high odds, laying at lower — which multiplies volume on a single event. The platform holds no risk at all: every position it books is offset by another customer, and revenue is a commission on net winnings.
为什么管用
A book needs balanced flow, and an exchange balances itself: every back can be met by a lay, so the platform never holds inventory. Competition among traders to get matched compresses spreads toward the commission — the study found exchange prices at once weak- and strong-form efficient, meaning customers received close to true probabilities. In-play trading multiplies transactions per event, and the best prices attract liquidity in a cycle fixed-margin bookmakers cannot answer without repricing their whole book.
值了多少
Exchange odds passed weak- and strong-form efficiency tests; commission up to 5% of winnings replaced bookmaker margins averaging 25.63%
什么时候会失灵
Matching needs liquidity — in thin markets spreads stay wide and volume never ignites. Risk is transferred to customers who may be worse at bearing it, and the paper estimates about 2.5 percent of turnover was attributable to insiders trading on private information. Regulators can kill the model: bookmakers lobbied that exchange layers were unregistered bookmakers, and tax regimes built on margins disadvantage commission-based platforms.
后来呢
The Economica study became canonical in betting-market and prediction-market research; exchanges forced bookmakers worldwide to sharpen prices, and the match-backer-against-layer-for-commission model spread from sport into financial and political prediction markets.
资料来源
- [1]Market Efficiency in Person-to-Person Betting (Economica 73)Economica / Nottingham Trent University repository, 2006irep.ntu.ac.uk