Betting exchange

Every bet matched on an exchange has a user on each side. One backs a selection at a price, another lays it, and the exchange matches the two and holds both sides' money until the market settles. Because users set the prices, a busy market's back and lay prices sit close together, and the exchange earns from commission on net winnings.

Say one user backs 10 units at 3.1 and another lays it. The exchange holds the backer's 10 and the layer's liability of 21. If the selection wins, the backer collects the 21 less commission. If it loses, the layer collects the 10 less commission.

The lay side is what matched betting needs, since a bookmaker only takes back bets. Money matters as much as price, because a lay is matched only against what other users have put up at that price, and on a quiet market that can be very little.

In the OddsRelay feed

The feed pairs bookmaker prices against the four exchanges, Betfair, Smarkets, Matchbook and BETDAQ. On the matched feeds each lay offer names its exchange in lay[].exchange, beside price, available and link. GET /v2/bookmakers lists every bookmaker and exchange key the API serves, each with is_exchange, true for an exchange, so a tool can tell the two kinds apart without keeping a list of its own.

Filters follow the same split. The exchanges parameter on a matched feed narrows the lay side to the exchanges a user has accounts with, and an exchange key sent as a bookmaker is refused with an error naming the right list. On the dutching feed type either list takes either kind, since a leg can be an exchange's back price.

On raw, an exchange's outcomes carry back_price, lay_price and available together, where a bookmaker's carry a single price, and exchangesOnly=true returns the exchanges alone. Exchange prices move as users add and take money, and meta.last_seen on a matched feed gives each exchange's last read per sport.

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