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.
Betfair is a British gambling company founded in 2000. It operates the world's largest online betting exchange. Its product offering also includes sports betting, online casino, online poker, and online bingo.