How Iphone's selling in cheap rate ( 11,12,13,14,15)

So guys there is this TikTok guy Kamal Mobil repair tamrakar stall 53.. So my question is how these iphone get so cheap... He sell iphones like 11-15 .. also exchange with your any phone... But first he will validate the phone inspect all from display change to battery all... My friend bought 13pro in 60k ... Without exchange... So, why it got that dirt cheap ?? Also I saw a post yesterday again with 30-35k on iphone 12-13 😅 Btw I also use my friends iphone and it was just like normal and clean and new no any scratches or opened .. so how ?? Any business geek here ?? Who knows about this business model ??