Free spins and staggered bonuses – deposit x and get xx, then deposit xx and get xxx, then deposit xx and get another xx.
I agree with bonusguy, it is a shame casinos do not publicize the small bonuses added as one plays. Many do that, but I have yet to come across a banner or promo I can use to sell with.
It’s one of my pet peeves… I can presell retention, it helps in making that first sale, but retention is a secret it seems.