Does social media help you sell stuff?

Does social media help you sell stuff?   Judging from the amount of time and money being invested by large companies in social media you might assume the answer is beyond dispute.  Alas its not as cut and dried as one might hope.
I cannot point to any empirical evidence (that's trustworthy) to validate either side. You'll have to wait for a study from a group who can  frame the question(s) -- i.e. study the matter scientifically in the first place.  They must clearly  understand and articulate what's being measured or the answers are anecdotal at best.
So what do we know?
Madison Avenue has thrived on this basic premise.  Repetition builds familiarity and familiarity breeds acceptance.   Either you buy that or you don't.  Most people do buy it which leads to the question -- "what's the best way to deliver the initial message?".
Look at two separate examples from the auto industry regarding Facebook hat occurred within 9 months of each other.   
  1. GM  famously pulled all its ads from Facebook just before the IPO saying that it found   evidence the platform's ads [had] "little impact on consumers' car purchases".
  2. Lexus got 100,000 views in 10 minutes for the video unveiling of its 2014 models at the January North American International Auto Show.  It got 600,000 views later in that same day. 


So why did GM pull its ads just before Facebook's stock offering and how can Lexus find such value in the platform less than 9 months later?  
Brian Smith, Lexus VP Marketing said  "the News Feed is why we got so many people to see it live, and it was kind of a game changer". "We loved it"  he said.
How can the two companies experience be so divergent?
GM was looking at the data after placing text ads or paid promotions on Facebook.  These are the ads that end up in the right column ghetto which have been show over and over to be easily ignored and discounted.  They are also not video.   On the other hand Lexus is talking about video content that shows up in peoples news feeds right where they're focused.  Assuming the content was a glorified advertisement for Lexus then it would be hard to see how viewing the content on one's Ipad or IPhone would be that much different than the same content in a TV commercial.
A view is a view  according the Lexus experience and I would agree.   GM on the other hand could not find any evidence that they're text ads were actually being seen by the people who viewed the page.  So if the ad was never actually recognized in the  viewer's mind there was nothing to repeat and acceptance cannot proceed.   Where Lexus was able to measure clicks and eyeballs the data for GM would have been ambiguous at best.
Note that almost one year later GM is back on Facebook.