New - used - no reason to differentiate between the two in my opinion. There are many LBS's that have eBay stores and sell their wares there simply because it's a great place to liquidate stock that has a hard time selling in the physical store itself. Other eBay stores are authorized outlets for certain companies. Again, there's absolutely no way whatsoever to determine an exact or even roughly approximate percentage. And frankly, I'd feel far more comfortable buying a new bike than a used one.
It sounds to me like the writer of the article has a questionable agenda all his/her own.