Bought an iPhone 6 from a friend - iCloud question
It's not clear what you mean by you've deleted their Apple ID and iCloud account from the phone, but if you've fully signed out of all services (i.e. Apple ID, iCloud, iTunes and App Store) then you're on the right track.

However, your friend needed to follow some steps before selling you their phone. According to Apple, this is what someone should do before they sell or give away their iPhone, iPad, or iPod touch.

I would start again by getting together with your friend and double-checking that everything is done the way it should be.