How do you ensure that the handsets are functioning?

Our testing includes strict checks of the IMEI (against the GSMA Stolen/Lost database), case condition, screen condition, buttons, headphone ports, earpiece, speakers, microphones, touch screen, LCD, WiFi connectivity, Bluetooth, camera, SIM reader and network connectivity, USB port, battery, accelerometer and finger-print reader (if applicable), appropriate software detection and blacklist checks. In total we make up to 90 individual checks across different devices. Should a handset fail any one of these tests, we simply do not sell it.