For Mac's:
- Apple Hardware Test
http://support.apple.com/en-us/HT201257
- Check Battery Status
http://support.apple.com/en-us/HT201585
- Check the HD (with Disk Utility)
- If there is an optical drive test it
- Check for any damage on the Mac
- Be sure Find my Mac is disabled
For iDevices:
- Check if there is an activation lock
https://www.icloud.com/activationlock/
- Check all the ports (headphone jack, lightning or 30 pins connector)
- Check Sleep/Wake button aswel the Home Button
- Check for any damage on the iDevice
- For iPhone 5S and higher, iPad Air 2 and iPad Mini 3 check if Touch ID works.
- Be sure Find My iPhone is disabled
- Be sure the owner is logged out EVERYWHERE (App Store, iTunes, iCloud,