A browser extension that searches for coupon codes is funded by affiliate commissions. How it earns them has been the subject of sustained dispute within the industry.
The extension acts at the moment of checkout
When a shopper reaches a cart page, the extension recognizes the retailer and offers to test stored codes against the order.
Testing codes requires applying them to the live cart, which is straightforward, but the extension also has an opportunity to set its own affiliate cookie at that moment.
Because most affiliate programs credit the last referring link, a cookie set at checkout can capture the commission for a sale the shopper had already decided to make.
Last-click attribution is what makes it possible
Affiliate networks credit the final referral in the chain, a rule adopted because it is simple to administer and hard to dispute.
That rule was designed for a world of links clicked before shopping, not for software present at the final step of every transaction.
Content publishers who introduced the shopper to the product argue the credit is being taken from them, which is the core of the complaint.
Merchants have their own concerns
A retailer pays commission on a sale that would have happened anyway, which converts an acquisition expense into a cost on existing demand.
Some merchants therefore exclude coupon and loyalty publishers from their programs, or pay them a reduced rate compared with content sites.
Others actively use extensions to recover abandoned carts, since a code offered at the hesitation point can complete a sale that would otherwise be lost.
Network rules have tightened
Affiliate networks now impose disclosure requirements on how extensions attribute sales and prohibit some behaviors, such as setting a cookie without user action.
Enforcement varies, and the technical detail of when a cookie is placed is difficult for a merchant to audit without instrumentation.
Browser vendors have also restricted extension permissions over successive releases, which limits what an extension can do silently.
The shopper's position is mixed
An extension that finds a working code delivers a genuine saving, and testing codes automatically is faster than searching manually.
The cost is a permission grant covering browsing on shopping sites, so the value exchange includes data as well as attention.
Understanding that the tool is funded by commission rather than by subscription explains both why it is free and why its incentives are not identical to the user's.