Affiliate networks usually charge an initial setup fee for each merchant and often a recurring membership fee. It’s also common practice for affiliate networks to charge merchants a percentage of the commissions paid to affiliates.
It’s in essence free marketing and advertising since the affiliate is the one who produces the lead without any up-front cost to them. This is also why CPS payout commission percentages are so high.
The Conversant, Inc. companies include Commission Junction, Dotomi, Greystripe, Mediaplex, and ValueClick Media.