Apple.com or Apple store.
Sure, you’ll be paying full price, but then you know you won’t be cheated. There are so many scammers out there that it’s just ridiculous.
I personally fell for one. Seller claimed it’s a new iPhone, but when I received it, the box is fake and the iPhone itself was already registered under someone else’s name and its warranty has expired when I check it with Apple. And this is from a legit e-commerce, not a Craigslist or something like that. Good thing they had proper return policy so I got my money back.
Costco! I picked up one of the XR during their Christmas sale where they gave you a trade in for a phone and then a rebate up to $750. Traded in a iPhone 6s Plus got a $80 bill credit and a gift card for the balance of $670. No monthly credits for 36 months. Only thing is you have to pay the phone out right at Costco. Once you get your rebate you can cancel service. Much better than the T-Mobile stores where the rebate is via monthly bill credit