Use this before the checkout page
If a purchase or switch is expensive enough to annoy you later, it deserves ten minutes before checkout. The goal is not to research forever; it is to catch the obvious wrong-fit decision.
Ask what would make this a bad buy
List the two or three things that would make the purchase fail: wrong size, hidden fee, poor return route, contract length, cleaning burden, compatibility or serviceability.
Check proof and responsibility
Find who sells it, who supports it, what the return route is and what evidence backs the key claim. If responsibility is unclear, pause.
Check the route, not just the product
Many bad purchases happen because the buyer used the wrong route: product page instead of checklist, provider page instead of renewal check, hotel page instead of cancellation check.
Use UK Shortlists next
Start with Before you buy or Find my shortlist. The site is built to route you into the right checklist before you open merchant pages.