All new users need to do is create an account with Betfair, deposit and place a 5 qualifying bet on any of their sports betting markets with odds of 1/2 (1.50) or higher. Once this is settled, players will then receive their 20 in free bets, to be able to be used on any of Betfair's sports markets.
Betfair isn't purely a no deposit bonus casino, but from time to time you may find free spins no deposit offers. Or small cash drops, either through a casino bonus code or from leaderboard tournaments. However, you'll more commonly find deposit bonus offers rather than free casino bonus offers.