Check the price first
An explainer on how price comparison works: what engines aggregate, how they earn money, and how to verify a listed price before buying.
A shop, a price feed, a retailer endorsement, or a claim about any specific company trading under a similar name.
It compares offers, not products — the same item listed by different sellers under different terms.
A comparison shopping website is a vertical search engine that shoppers use to filter and compare products based on price, features, reviews and other criteria. The engine itself does not hold stock. It pulls product data from retailer feeds and normalises it into a single row per offer.
That normalisation is where the first gap appears. A seller may list a 1.5 V battery in a 4-pack, another in a 12-pack, and a third as a single unit. Unless the engine converts to a unit price, the cheapest row on screen can be the most expensive per item.
The second gap is terms. Price is one column; shipping, tax, delivery window, stock status and return policy are separate. Two rows showing the same number can cost very different amounts by the time the parcel arrives.
Mostly from affiliate agreements: the retailer pays the site a share when a visitor clicks through and buys.
Comparison shopping sites typically earn money from affiliate marketing agreements. The site does not charge you to search. The retailer pays a commission on completed sales that originated from a click on the comparison page.
This is a legitimate model, but it has a structural consequence: the site is paid by the sellers it lists. A retailer with no affiliate programme may be absent from the results entirely, not because its price is bad but because there is no commercial link to track.
In the United Kingdom, comparison shopping services made between 780 and 950 million pounds in revenue in 2005, which shows how large the affiliate-funded model had already become at that point. The revenue came from retailers, not from shoppers.
| Field | Typical value | Unit | Failure if missing |
|---|---|---|---|
| Headline price | £24.99 | GBP | You compare incomparable numbers |
| Pack size | 4 units | count | Unit price is wrong by 3× |
| Unit price | £6.25 | GBP per unit | Cheapest row is not cheapest |
| Shipping | £3.95 | GBP | Landed cost jumps at checkout |
| Tax | 20% VAT | percent | Cross-border totals mislead |
| Stock status | In stock | status | You click through to a dead page |
| Return window | 30 days | days | Cheap price hides return cost |
| Feed age | 18 hours | hours | Listed price is already stale |
Because result order can be paid placement, a ranking formula, or a mix of both — and the page rarely tells you which.
Some engines sort strictly by price. Others sort by a score that includes commission rate, retailer reliability and conversion history. A few sell the top slot outright as sponsored placement.
If you cannot tell which rule is in force, treat the order as advertising until proven otherwise. The check is simple: sort by price ascending yourself, then compare the top three rows on total cost rather than headline cost.
A useful habit is to open the same product on two different comparison engines and on the retailer's own site. If the three disagree by more than the shipping cost, at least one feed is stale.
Sources are limited to the published definition and the revenue figure cited; no retailer, price or person has been invented.