A pre-checked box at checkout is a classic dark pattern — it uses default settings to opt you into extras you might not want. Design researchers call this a 'manipulative default' because most users accept defaults rather than read fine print. The pre-checked box might add insurance, a 'premium' shipping upgrade, a donation, or an add-on service that tacks another recurring or one-time charge onto your order. The psychological trick is subtle: users assume checkboxes reflect their active choices rather than defaults set to benefit the seller. The practical defense is scan-and-uncheck: train yourself to pause at each checkout screen and inspect every checkbox, toggle, and pre-selected option. Make it a habit to click 'show details' or 'view pricing' before completing purchases.

Technical tools can help but are imperfect; browser extensions exist that highlight pre-checked boxes or block certain scripts, yet the simplest defense is behavioral: slow down and use the mouse to hover and read the fine print. If you frequently order from a vendor that uses pre-checked add-ons, consider saving a template in a password manager with preferred settings or check your account defaults ahead of time so the vendor can't surprise you at purchase time. For subscriptions discovered via pre-checked offers, request and keep cancellation confirmations and watch your statement for the first renewal charge. If the vendor resists cancellation, escalate to the platform (app store), your card issuer, or the regulatory complaint channel in your jurisdiction as appropriate — but usually the most cost-effective step is the initial habit change: uncheck.