Hitman, basically but details can vary
affiliate drives traffic and post-up players (referrals). can get a % of sign-up, % of losses, or CPA (cost per acquisition)
an agent vouches for credit players, acts as a go-between form the book to the player. He is also guarantees cash to both sides of the counter...if the book stiffs, he is responsible for paying his players. If a player stiffs he is responsible for paying the book. In return he gets a % of player lossses (higher than an affiliate)