Betfair will never ban anyone for being too successful as they are still getting their commission - you are winning money off other punters not from Betfair (of course you may get banned if the reason you are winning is because you are cheating!).

I know of numerous people that have been banned or severely restricted (eg. $20 maximum bets!) from Tennis betting with various bookies - generally the ones based in England seem to have the worst reputation for this with the Aussie bookies appearing to be more tolerant of winners.

As far as horse racing there was someone on another forum complaining about edited limiting his racing betting (another English bookie in disguise!) but have never heard of any complaints against IAS. (I think Mark Read is smart enough to realise that a consistantly winning punter is a good thing - they tell you what horses you need to lay off with other bookies!).

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"Computers can do that????" - Homer Simpson