I purchased a renewed iphone off amazon. Of course there are many used on fb buy and sell or kijiji and I would buy used from those places as well. Besides the obvious external condition and operation go into the settings and check the battery health. Is it unlocked? You'll want to know if the phone was stolen as well. If it looks good, works good, not stolen and the battery is not an issue I would buy. So many people disposing of perfectly good phones just to get a new phone with a new contract.......makes me happy
https://appletoolbox.com/check-iphone-stolen/