Sunday, 20 June 2010

Double Crossing

One of the consequences of Betfair’s cross-matching algorithm is rather odd.
In a binomial market, a request to back at 2.0 results in an opposing lay at 2.0, but when the numbers are rounded, strange things happen.

For example, a back of Alpha at 1.85 results in an opposing lay of Beta at 2.16. Enter a lay at that same price of 2.16 on Beta, and the opposing back for Alpha appears at 1.87.

Not only that, but you can have a market where there is money to back Alpha at 2.16 and at 2.18. The 2.16 was offered first and is there as a result of an opposing request to back Beta at 1.85, while the 2.18 was entered as a lay of Alpha, with an opposing lay displayed at 1.85.

Hang in there; I do have a point.

Now, if someone decides to lay the 1.85, they are matched with the money at 2.16 first, NOT as you might expect, with the money at 2.18.

Apparently Betfair do NOT always give you the best price available, despite what they claim.

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