There's an important difference between Facebook advertising and Google advertising in this context. The Google ads from the Ebay experiment are search ads, i.e. a user searches for "ebay shoes" and then Google shows a combination of both paid ad links as well as organic search results. Because of this, many of the users who click the ad might have clicked on the organic link if ad spending was cut off. Thus the ROI on is low/negative, especially for "branded" searches like this (where the user is already looking for your site by including "ebay" in the search query).
Facebook ads are not search ads. They are display ads. (You should correct the description in your article). These are ads shown in the user's feed. If the brand stopped advertising there is very low likelihood that similar links for the same product would have shown up "organically" in the user's feed. This is a big reason for why the Facebook ads had a clear positive effect (if you cut off facebook ads you will get substantially less traffic) vs. Google search ads where many of the users would have gotten to your site regardless of the advertising.
There's an important difference between Facebook advertising and Google advertising in this context. The Google ads from the Ebay experiment are search ads, i.e. a user searches for "ebay shoes" and then Google shows a combination of both paid ad links as well as organic search results. Because of this, many of the users who click the ad might have clicked on the organic link if ad spending was cut off. Thus the ROI on is low/negative, especially for "branded" searches like this (where the user is already looking for your site by including "ebay" in the search query).
Facebook ads are not search ads. They are display ads. (You should correct the description in your article). These are ads shown in the user's feed. If the brand stopped advertising there is very low likelihood that similar links for the same product would have shown up "organically" in the user's feed. This is a big reason for why the Facebook ads had a clear positive effect (if you cut off facebook ads you will get substantially less traffic) vs. Google search ads where many of the users would have gotten to your site regardless of the advertising.
PS you have a typo in Dan Chapsky's name.