I knew (read, I thought I knew
) the above was not true... so I looked it up and found the following:
Will there be unmatched SP bets if the money isn’t there?
In theory, there could be unmatched SP bets. We don’t actually guarantee a match. But this would only happen if the price is 1.01 or 1000 – the two extremes of our SP. If 1.01 were the final SP, then some backers might be unmatched. If 1000 were the final SP, then some layers will be unmatched. However, we expect this to be very rare.
Then a little further I find the following:
If I specify a limit on an SP bet and the calculated SP is equal to my limit am I guaranteed to be matched?
No. To include all SP limit bets which have a limit exactly equal to the SP in the reconciliation process and match them could result in an imbalance between backers and layers. Therefore where an SP is calculated that is exactly equal to backers’ and/or layers’ limit SP bets none, some or all of those bets may be included. In this event SP limit bets with identical limit prices will be matched on a first come, first served basis as is the convention in Betfair’s Exchange markets. Lay bets with a higher limit and back bets with a lower limit will definitely be matched.
And some more why SP bets might be cancelled:
Can I request to ‘Take SP’ on an unmatched lay bet if my liability is less than £10? (Minimum liability)
Yes, but at the off if the liability on the bet is less than £10 the bet will be cancelled and will not be included in the SP reconciliation.
For example: As an Exchange layer I decide to lay a horse for £5 @ 2.0. It is trading at 3.0 so my bet is unmatched. I then request to ‘Take SP’ at the off if my bet is still unmatched at 2.0. The system will allow this request but if unmatched at the off it will lapse. Also, if a customer for example asks to lay £50 at 1.5, convert to SP if unmatched, and £40 gets taken leaving £10 lay at 1.5 the balance will cancel at the off. It will not convert into an SP lay bet as the revised balance at the off was less than the minimum £10 liability allowed for SP bets.
So, in short, in theory, if you place your order correctly for the right amount, you will get matched.
Personaly I think that especialy small traders might bump into that 10 pount limit....
All info above comes from here:http://promo.betfair.com/betfairsp/FAQs_theBasics.html