The decoy effect — formally asymmetric dominance — steers a choice by adding a third option that is deliberately worse than the option the seller wants you to pick. First documented by Huber, Payne, and Puto (1982) and later popularized by Dan Ariely, the effect works because human beings are poor at judging absolute value and skilled at judging relative value. When two genuine options are hard to compare, a well-placed inferior option gives the mind an easy comparison to make — and the option that clearly beats the decoy suddenly feels like the obvious winner, even though nothing about it actually changed.
The classic demonstration involves three subscription tiers: a cheap digital-only plan, an expensive print-only plan priced almost identically to the top plan, and a print-plus-digital plan. The print-only tier is the decoy; almost no one chooses it, and it exists only to make the combined tier look like a bargain by comparison. Remove the decoy and preferences shift. The mechanism is contrast, not merit: the decoy is dominated on every dimension by the target, so the target looks generous, while the cheaper honest option quietly loses ground it should not have lost.
As recognition, the tell is a tier that makes no sense as a purchase — an option no informed buyer would take, sitting conspicuously next to the one the layout pushes hardest. Because the harm per instance is usually modest (a few dollars of upsell rather than fraud), the effect is more a nudge than a con, but its ubiquity across menus, pricing pages, and plan selectors makes it worth spotting. The defense is structural rather than emotional: define your own requirements before you look at the arrangement, judge each option against those requirements alone, and the planted comparison loses its grip.