There's no way to quickly determine who is an expert.
But, there is a quick way to determine everyone who isn't one.
Just identify people that identify themselves as "experts."
It's absolutely impossible to be an expert in any emerging or rapidly changing field like social media or blogging or even the publishing industry. (It's particularly amusing to me that all these social media "experts" only have 900 or so Twitter followers. Wow, start taking your own expert advice, buddy.)
Thus, any one who says they are an expert is full of shit.
You can be an expert in Latin or the Civil War or Negro League baseball, sure. That shit isn't changing.
But, anything modern, anything that's still forming and developing and fluid...no experts exist in the entire world.
So, come to think of it, I actually am an expert in one thing:
Noticing all the experts that have no expertise.