We’ve started tracking 3 prices until Black Friday — and sealing every change
Today, 8 October 2026, we are starting an experiment at Sellat: checking the price of three products until Black Friday 2026 and recording every change in a verifiable history, one that cannot be rewritten later to fit whatever happens.
We are not trying to prove that a store cheats, or to predict what will happen. We want to observe and, when Black Friday comes, compare the price advertised that day with the price these products showed in the weeks before.
Updates
- 8 Oct 2026 · Day 1: we registered the starting price of the three products.
The three prices we are tracking
| Product | Observed price | Reference |
|---|---|---|
| Samsung OLED 55″ TQ55S90HAEXXC MediaMarkt | €1,099.00 | €1,999.00 (−45%) |
| ASUS TUF Gaming A16 FA608UHI-TU232W Fnac | €1,199.99 | €1,599.99 (−25%) |
| Roborock Q10VFP52-00 with dock Carrefour | €285.00 | €399.00 (SuperChollos) |
How we record each change
Each product has a public history on Sellat. When we detect a change, we add a new version with the observed price, the reference price shown by the store and, when there is one, the advertised discount. If a product has no new version, it means we have not recorded any change.
Each version has its own SHA-256 fingerprint, is chained to the previous version and is anchored on a public network. That is why we cannot reach Black Friday and rewrite what we saw weeks earlier: the history already exists. It is the same proof of existence Sellat applies to any file.
What we want to find out
Something very simple: what price did the store show before Black Friday? On 27 November we will be able to see:
- whether the price really went down, or had been lower a few weeks earlier;
- how the reference price and the advertised discount changed;
- or whether nothing particularly interesting happened.
Any of those outcomes is valid. The goal is not to prove a conclusion decided in advance, but to record the data before we know the result.
How can you tell if a Black Friday deal is real?
The hard part of judging a promotion is remembering what the product cost a few weeks ago. A price history lets you compare; a verifiable price history adds something more: earlier observations cannot be changed afterwards to fit the story someone wants to tell.
A seal does not prove that a price is correct, nor that the store did not publish other prices. It proves what we recorded and when, and that we have not touched it since.
Today is day 1. Let’s see what happens.