Why Don't Google's Seller Ratings Add Up?

Browsing Google Product listings recently, I noticed that the seller ratings seemed much higher than you would expect based on the breakdown of reviews provided. Companies with many 1 star reviews seemed to enjoy quite high averages which didn’t seem to add up. In the interests of science, I took a closer look.

I searched Google for [television], selected the “products” tab and then clicked on the first result. As it turns out, a rather nice LED TV. This page then displays the top 10 “most relevant” sellers:

Top 10 most relevant sellers in a Google Product search

These pages then contain a seller rating:

Average seller rating

..and also a breakdown of review scores:

Breakdown of star ratings

So far so good. I collated the data from the top 10 sellers, and then worked out an average – total stars/number of reviews. This is the arithmetical average stars. Here’s the breakdown vs Google’s own average:

RankSellerAverageBased onGoogle’s averageBased onDifference
6Richer Sounds3.4764.5761.1
9RGB Direct4.41,3604.413620.0
10365 Electrical2.9854.5851.6

So, in all but one case, Google’s average is quite a bit higher (on average, 13% higher) than would be expected based on the pure numbers. In no case was the arithmetical average lower than Google’s. In one case, a seller with forty 1 star reviews, thirty-six 5 star reviews and nine in between displays a 4.5/5 average in Google. This just doesn’t seem right.

Why are the ratings always higher?

This is the interesting question. Google themselves offer this explanation:

“We calculate Seller Ratings using a variety of signals beyond just the arithmetic mean in order to make sure Seller Ratings reflect not only the raw quantity of review scores, but also how representative and high-quality the reviews are. We’re constantly refining how we use those signals to give our users as helpful an overview as possible.”


So, they’re using a weighted system of some kind. But why would it seem to always be higher?

Some sources get more weight than others

This idea can be all but discounted entirely, since even when reviews come from only one source, the average is not as would be expected.

Positive reviews are of higher quality

Perhaps Google’s weighting has determined that higher quality reviews are “better” than lower quality reviews. But that would seem to be slightly counter-intuitive. Although perhaps someone is more likely to submit a negative review than a positive one. It would then be a question of how the weighting occurs.

Similarly, it’s possible that Google uses text analysis which has discovered negative reviews to be of worse quality. But then, if you’re very unhappy, perhaps your writing skills will also be affected 😉

Positive reviews are given more weight arbitrarily

The more cynical among you will point out that seller ratings are displayed in Adwords:

“If your online store is rated in Google Product Search, you have four or more stars, and you have at least thirty reviews, you’ll automatically get seller ratings with your ads.”


And those ads with positive reviews get a much greater clickthrough rate:

“On average, ads with Seller Ratings get a 17% higher CTR than the same ads without ratings.”

So, is it some kind of clever sentiment analysis? Some kind of other text quality assessment? Or is this just a ploy to attract more clickthroughs? Whichever it is, caveat emptor if you are using Google Products and factoring in seller ratings into your decisions.

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  1. Wow, that’s really interesting reading. As Trip Advisor have just been asked to remove the word “trusted” from their reviews (by the ASA) I think Google will at some point have to come clean on exactly how this metric is caluclated.

    It’s very worrying that the Google score is always higher, especially when w’ere talking about such as small range as 5 stars, to get an extra star thanks to the algorithm seems very wrong.

    The only filter Google should ethically use is one to remove reviews they deem to be fake (such as this software http://news.cnet.com/8301-17938_105-20083200-1/cornell-software-fingers-fake-online-reviews/) – anything else is an abuse of customer trust.

    When people see the stars they take it on face value and assume it’s an average. If it’s not a fair average then people are being decieved. If the ASA were notified of this I doubt Google would have a leg to stand on.

  2. Glad I’m not the only one who noticed this, you’ve done a fantastic job of capturing the issue,

    We have an example of a lower rating, our G+ page for tech support and services has only 5 star reviews (we’re still new), but an average of 4.8…….!

    We’re call Digital Plumbing, you can find our google+ page, won’t post a direct links as we aren’t just trying to get free backlinks.

    What’s your thoughts on our example being 0.2 negative to our true average review scores.

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