How does Apple feel about buying/selling their used products?

Question

Apple

Hello.
For the New Year, I want to make myself a small gift - to buy an iPhone 6 / iPhone 6 Plus, I don’t know anything about this at all.
I know that there is iCloud, so does Apple support the resale of their products? Or does the company mind?
And another question - what should I check with the iPhone when buying? How to completely untie the old owner on paper / from the phone? If the owner signs out of iCloud, can I create a new account?

Answer 1

Apple does not care about resale, donation, etc. of its technology.
https://support.apple.com/ru-ru/HT201351 and pay attention to this.

Answer 2

If the owner logs out of iCloud, then you can do anything with the device:
1. Reflash
2. Update
3. Sign in to your Apple ID
, etc.