Although all exchange does the same, they do charge very low fee compared to luno
When you buy at a price, your selling price should include both the fees and your profit
You buy BCH for $100
Price increased. The worth is now $150. If the fee is $1, then you will have $49 as gain.
You can decide to sell the same $150 worth of BCH for a price of $160.
The actual worth is $150, but you are selling it for $160.
If the fee is $2, then when you sell, you will have $58 as gain.
The initial amount you bought was $100. By virtue of the price increase, the $100 rose $150 in value. You can decide to sell at this amount. Or you can place a sell order for even a higher price, let's say $160. When you sell, the fee may be $2. I don't really know how much fees are charged.
From there, you should know how much you can earn.