Can an iPhone be used after a Find My iPhone erasure?
It seems like Activation Lock does make erasing harder starting with iOS 7.

Find My iPhone includes a new feature called Activation Lock, which is designed to prevent anyone else from using your iPhone, iPad, or iPod touch if you ever lose it. It starts working the moment you turn on Find My iPhone in iOS 7
Even if you erase your device remotely, Activation Lock can continue to deter anyone from reactivating your device without your permission.

However there several methods that enable you to bypass this activation lock. Simply google for bypass activation lock iphone.