Once a referred user has joined the marketplace, they can apply to become an affiliate (if the marketplace owner allows it). If approved, they will receive their own unique referral link and can start promoting the marketplace to others.
From that point on:
They act as a Referred User in relation to the affiliate who originally referred them
They act as an Affiliate for any new users they refer themselves
This allows referrals to create a natural growth loop, where users can both participate in the marketplace and help promote it.