Social selling is targeted social media. It's social media with a VERY clear target and absolutely measurable ROI.

Social media, in general, can be good when there is value to creating and nurturing a persona that wants to "belong" to a community. Some products and services work like that. It's a club that self identifies as "engaged with the brand".

But that's not "of value" for lots of business models. There's just no real ROI without a targeted strategy that integrates "social" as an effective selling or brand building tool with real measures of effectiveness.