In this video, Motley Fool tech and telecom analyst Andrew Tonner tells investors about a recent study from a group of economists at eBay's (EBAY -0.45%) Research Labs, comparing geographic areas where the company had withdrawn its Google (GOOGL 1.56%) ads with areas where it hadn't over a three-month period. The company found no significant loss in sales between the two areas. Does this call into question the efficacy of advertising with Google? Andrew tells us why having a major advertiser like eBay lose faith might have an impact on Google, and he gives investors some key takeaways for their own investing theses on these two companies.