I have a question related to Business Model.
Let's say I have an $x$ number of products with fixed cost. The cost of products can range from low to high. I also have the purchase amount for those products and listing amount for those products i.e the selling price of those products.
I want to calculate a cart such that I always gain a certain unit money on that cart or a certain percentage of the total amount on that cart. I can add an amount $y$ to the cart in order to change the final profit amount.
How do I approach this solution? Also calculating with fixed unit money is a good idea or calculating with fixed percentage?