ATT isnt going to blacklist it, at least they are not doing so any time soon.  But the previous owner could.   If you trust the seller and are buying through a legit website like eBay or Swappa, you don’t have to worry about ATT.

 If you unlock it, you will know if it’s paid off.

(The following is included after all posts to save typing) We are customers too, NOT employees. Our answers are based on experience and reading content available on the website. Our answers are honest, but not always appreciated. If you posted personal information, please edit and remove.

Google Alert – “iphone 7”