For this reason alone, Betfair has no reason to ban or close your account when you should win. This is what Betfair first became famous for; peer-to-peer betting. Whilst the Exchange account won't be closed for winning, there is an additional commission rate.
There are a number of reasons for which we suspend accounts: You have added a debit card to your account that is not registered in your own name. Your personal details already exist on another account. Information provided by you leads us to believe you are under the age of 18.