What's really important in Social Media Marketing?

Does social-media marketing work?
This has long been a question brands have tried to definitely answer. It has been brought to the fore of late by a recent Gallup poll, the report from which states, "A clear majority of Americans say social media have no effect at all on their purchasing decisions."
That may make it sound like social media marketing has little benefit, but the report's cursory dismissal doesn't take into account several other factors.
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