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.
This personalisation of the commission structure means customers have the choice to pay either 8%, 5% or 2% commission on Exchange winnings. The Rewards+, Rewards and Basic packages all comes with various add-ons to help tailor your Betfair experience to your preferred way of betting.