A marketplace listing with thousands of positive reviews may be showing a product that earned very few of them. Variation grouping is how the two become detached.
What variation grouping is for
Products that differ only in size or colour are grouped on one page so shoppers do not have to compare a dozen near-identical listings.
The grouping is legitimate and useful for genuine variants, since a review of a jumper in one colour usually applies to the same jumper in another.
Reviews are pooled across the group, which gives new variants immediate credibility from the accumulated feedback of the ones already selling.
Where the mechanism is abused
Because grouping is defined by the seller, unrelated products can be attached to an established listing so they inherit its rating.
A page that once sold one category of product can be edited to sell something else, carrying the existing reviews to an item nobody reviewed.
The reverse happens too, where a listing with poor feedback is repurposed after the seller changes, leaving criticism attached to an unrelated product.
How to spot a detached rating
Reading the recent reviews rather than the average is the quickest check, since the text describes what people actually received.
Reviews mentioning a product type unrelated to the page, or referring to variants that no longer exist, indicate the history does not belong to this item.
A sudden jump in review volume long after the listing was created is another signal, because organic feedback accumulates gradually rather than arriving at once.
Why platforms tolerate the ambiguity
Grouping improves the shopping experience for the vast majority of listings, and separating every variant would fragment reviews across thousands of near-empty pages.
Detecting misuse requires judging whether two products are genuinely variants, which is a matter of degree rather than a rule that can be applied mechanically.
Enforcement therefore relies on reports and on pattern detection, both of which act after the fact rather than preventing the change from happening.
What a rating is really summarising
An average rating summarises a set of transactions across time, sellers and versions, and none of those are guaranteed to match the current offer.
Dates, variant labels and the seller name give that context, and they are the parts of the page most likely to have changed since the reviews were written.
The rating is best treated as evidence about a listing's history rather than as a measurement of the specific product now shown on the page.