hi
betfair does not like you to bet below there minimum amount and in certain circumstances will close your account, i had my account closed due to betting below the limit and had to use my girlfriends name and credit card to have a new account,BUT i was betting with a certain system that was guaranteed to win, but with only .01 euro (many small bets make big money), they said that it was fraudulent actions that disadvantaged the back better.
so it is safer to bet above there limit, with a few bets below, just for testing a new system for a week or so.
mcbee