We all know, that iPhones costs a lot. Nowadays you can get much cheaper price, if you buy refurbished, for example Apple iPhone 6 refurbished price - 220 USD from E Bay ( memory - 16 GB, RAM 1 GB ) -
https://www.ebay.com/globaldeals. Is it profitable to buy refurbished mobile or no ?
What do you mean "is it profitable to buy..."? Are you planning to resell?
Get a new phone instead for that same money -
https://www.zteusa.com/axon-7mini/Compare them -
https://www.phonearena.com/phones/compare/ZTE-Axon-7-Mini,Apple-iPhone-6/phones/10222,8346 I just bought 2 of those and upgraded them to the Android 7.1.1
Marshmallow Nougat update ZTE pushed out. Haven't really tested them fully but so far I am impressed for the price.