1 · Half of what you're paying for can't do what you want
Discolouration is either extrinsic — a film on the surface — or intrinsic, meaning it's the colour of the tooth itself. Only peroxide-based methods meaningfully touch intrinsic colour.
If your discolouration is intrinsic, no amount of surface-acting toothpaste, charcoal or purple product will change it. They aren't scams; they're solving a different problem than the one you have.
2 · A professional clean is the most underrated whitening there is
It removes extrinsic film comprehensively, in one appointment, and it's the biggest single visible change most people have available. It just isn't marketed as whitening, so it doesn't feel like the answer.
3 · The results photo wasn't taken in your bathroom
Controlled lighting, controlled angle, a chosen frame. Shade is the single most lighting-sensitive thing about a tooth.
4 · It reverts, and the rate is the real price
Extrinsic results come back as soon as the habits that caused them resume. Intrinsic results drift more slowly but still drift.
Nobody advertises the reversion rate, which means nobody advertises the annual cost. If you track it yourself, you find out in about eight weeks — and that number, not the sticker price, is what the product actually costs you.
5 · Sensitivity is a real trade, not a defect
Peroxide works by penetrating enamel. For some people that produces sensitivity, and "no sensitivity" on a label very often means "no peroxide", which very often means extrinsic-only.
The thing that fixes all five
Measure before, during and after, in the same light, at the same time of day, weekly. Every one of these five stops being a matter of opinion the moment you have a slope.