Complaints by users of the declining quality of search engine results contain a seed of truth, according to a recent study released by a group of academic researchers.

The researchers from Leipzig University, Bauhaus-Universität Weimar, and ScaDS.AI — all in Germany — concluded that “all search engines have significant problems with highly-optimized (affiliate) content.”

In their paper titled “Is Google Getting Worse? A Longitudinal Investigation of SEO Spam in Search Engines,” the researchers, by monitoring Google, Bing, and DuckDuckGo for a year on 7,392 product review queries, found that although they could not predict where individual pages would be ranked, they could conclude that “higher-ranked pages are on average more optimized, more monetized with affiliate marketing, and they show signs of lower text quality.”

One of the problems with the study is that it’s confined to product reviews. “Think of it like this: if you only walk down one aisle in a big store, you’re going to miss a lot of other stuff in the store,” said Nazmul Hasan, founder and CEO of Microters, a provider of digital marketing and software development services.

“The study mostly found websites that are trying to sell things, often with special links that make them money if you buy something,” he told TechNewsWorld. “This means they were more about selling than just giving good, plain information. It’s a bit like when you ask for help, but everyone just tries to sell you their things instead.”