What is happening with an item itself when customers returns it for any reason?

I only get an email from amazon that customer’s refunded and amazon deduct money from payments. I consider returns as a loss in numbers but what is actually happening with the returned items itself? Amazon through them straight into the bin or sell themselves at a cheaper price ?

Sometimes it takes 50 sales to get $100 profit but then 2-3 customer returns for any reason eat all the profit.