EBay study questions value of Google's main ad service

EBay, one of the biggest Internet advertisers, released a study examining whether the paid search ads it bought on Google and that show up to the right of search results were worth the investment.

"The conclusion: Incremental revenue from paid search was far smaller than expected because existing customers would have come to eBay regardless, whether directly or through other marketing channels," eBay spokeswoman Johnna Hoff wrote in an email to Reuters on Tuesday.

The study highlights a potential problem for Google, which generated USD 46 billion in ad revenue last year, up from USD 38 billion in 2011.

Some leading e-commerce companies, such as eBay and Amazon.com Inc