A demo is built to hide friction, not show it. That is not unique to AI, every product category has always done this, but AI demos hide friction unusually well because failure often looks like a plausible, confident, wrong answer rather than an obvious crash. A broken app freezes. A wrong AI answer just sits there sounding fine.
A few concrete checks separate a real capability from a staged one. First, ask whether the demo shows the tool's fifth attempt of the day, tired and sloppy, or its best possible input, carefully typed once. Second, look for whether the video shows the tool being wrong and recovering, not just being right the first time. A team confident enough to show a correction is usually further along than one that only shows a clean take.
The most reliable check of all: try the free version yourself, with your own messy, real, everyday request, not the polished one from the ad. If a tool only shines on the exact phrasing shown in the marketing, that is not a tool that shines, that is a script that was rehearsed. The free tools on this site are built to survive that test, on purpose. Try any one of them with the worst, vaguest version of your real question, not a tidy example.