This is a community exchange project; gift certificates, coupon numbers, serial codes will be distributed to the community and can be traded. So each user needs an account with the ability to transfer there gift certificate to another user.
Preferable on a joomla platform, lets say as a fireboard plug-in or vbullitin plug-in or as a ticket tracker.
A bit like karma points or drupal user points; simple coupon database to lodge credits.