Coupon sites are free to use and generate substantial revenue. Understanding where that revenue comes from explains most of what is frustrating about them.
The affiliate mechanism
The entire model.
Retailers run affiliate programmes paying a commission on sales referred by a third party.
Attribution is generally last-click, meaning the commission goes to whichever affiliate link was clicked most recently before the purchase.
Which means a coupon site does not need to have introduced you to the product, or persuaded you to buy, or even provided a working code. It needs your last click before checkout.
That single design decision explains everything else.
Why the codes frequently do not work
Follows directly.
A site benefits from your visit regardless of whether a code works, provided you click through and complete the purchase.
Which removes most of the incentive to maintain code accuracy, and expired or invalid codes are listed alongside working ones with no clear distinction.
Some sites display success rates or recent confirmations, which is a genuine improvement and is not universal.
The practical consequence is that the process of trying six codes, five of which fail, is not a failure of the site from its own perspective.
The interception problem
The more contested practice.
Browser extensions offering to find codes at checkout have been the subject of substantial controversy and litigation.
The allegation, made in several disputes, is that such extensions replace an existing affiliate attribution with their own at the final moment, capturing a commission that would have gone to whoever actually referred the customer.
Content creators and publishers who drove the original referral have objected, since the commission is taken after their work is done.
Cases have proceeded in several jurisdictions and retailers have adjusted programme terms in response.
Whether any specific extension does this is a matter for the specific evidence, and the mechanism is straightforward and the incentive is clear.
What this means for the shopper
Practically, mixed.
A working code is a genuine saving and the site provided it.
The commission is paid by the retailer out of margin rather than added to your price, so using one does not cost you directly.
It may cost somebody else — a publisher whose recommendation you followed — which is a consideration if you value that.
And the time spent trying invalid codes is a real cost that the model does not price.
Where codes actually come from
Worth knowing since it predicts which work.
Public promotional codes issued by the retailer for a campaign, which are widely distributed and generally work.
Affiliate-exclusive codes issued to specific partners, which work and are frequently only available through that partner.
Targeted codes issued to specific customers — abandoned basket recovery, win-back campaigns, loyalty offers — which are tied to an account and generally fail for anybody else.
And expired codes, which accumulate on aggregator sites indefinitely.
The middle two categories explain most of the failures.
The abandoned basket route
A mechanism worth knowing about.
Many retailers send a discount to customers who add items to a basket and leave without purchasing, generally within a day or two.
This requires being logged in or having provided an email address.
It works often enough to be worth trying on any non-urgent purchase, and it is a code issued directly to you rather than one found elsewhere.
The obvious limitation is that it only works if you are genuinely willing to wait.
What I actually do now
Check one reputable code source rather than several, since the marginal return on the fourth site is close to zero.
Try no more than two codes before giving up, since the time cost exceeds the expected saving beyond that.
Leave a basket for a day on anything not urgent.
And where a publisher's recommendation led me to something, use their link deliberately, since that is where the commission was actually earned.
The publisher side
Worth understanding since it explains the ecosystem.
Publications and creators earn commission on purchases made through their links, which funds a substantial amount of product journalism.
Which creates an obvious tension, since the incentive is to recommend things that convert rather than things that are best.
The publications that handle this well disclose it clearly, test independently, and recommend against buying where appropriate.
The ones that do not are recognisable by recommending something in every article and never concluding that a category is not worth buying into.
Browser extension permissions
Worth checking before installing anything in this category.
Extensions offering to find codes generally require permission to read and modify data on every site you visit, which is the access required to detect a checkout page and to insert codes.
That is a broad permission and it is granted to a commercial company whose revenue model depends on your purchasing behaviour.
Reviewing what an extension requests, and what its privacy policy says about what it collects, is a reasonable step before granting it.
The same applies to price tracking extensions, which need less access and sometimes request the same.