Buying used iphone 5s, lost phone?

I'm considering buying a used iphone 5s.
what's worrying me is can the seller on a bad day report lost phone? Because hes the original owner does he hold that power to report that the phone has been stolen? Or when you do a factory reset the new owner would hold this power?

This site has good advice on buying a used iphone http://www.justtext.com/messageboards/20140127095337.html

If the seller is the original owner of the phone, he can report the phone stolen. Always consider buying from someone who sells in bulk or a reseller. If you need used iPhone 5S at reasonable price and with safety, mail me.

Chris. No matter what iDevice you want, you need to check for this feature before you purchase it. If it is activated, don't walk, run away.
iCloud activation lock.
Best luck.
http://appleinsider.com/articles/14/10/01/apple-releases-icloud-tool-to-check-device-activation-lock-status

http://support.apple.com/.../kb/ht5818