Is it a scam
I heard recently that apple trade in iPhone 10 as a form of recycling for iPhone 6,7 and resell it again
So am asking apple community that is it possible
Apple does have a trade-in scheme, where you can trade in your device and receive a certain amount of credit off your next iPhone purchase.
I notice you've mentioned an iPhone 6 in your answer, Apple will not offer trade-in value for this device but they will recycle it for you for free.
https://www.apple.com/uk/shop/trade-in
If I have misunderstood your issue or can be of any further assistance, please let me know.