I spend a lot of time talking to new and scaling ecommerce sellers, and one mistake keeps popping up over and over. They lock in a selling price, load up PPC budget, and start sending inventory, without answering one simple question: how many units do I actually need to sell just to break even? Here’s the conversation I hear constantly: "I can sell this for $39.99, my variable cost per unit is $15. This product should print money." Then monthly fixed costs hit, ad spend burns, and they fi...