Here are links to some of our Help Guides which you might find useful:
Selling Your Phone
Buying a Refurbished / Pre Owned Phone
Top 8 Tips for Buying a Refurbished Phone
How To Guides
How to transfer data from your iPhone using iCloud
How to transfer data from your iPhone using iTunes
How to backup your iPhone to iCloud?
How to backup your Android phone to Google Drive?
How to backup your Samsung phone to OneDrive?
How to data wipe my iPhone / iPad?
How to data wipe my Android phone?