Service calls turn into cash drains when untracked hours and surprise parts eat your margins alive. The wrong job costing method, whether time & materials or fixed bid can hide 20-30% losses until jobs close, forcing you to chase payments or cut crew. Mastering these approaches isn't optional; it's how you turn reactive repairs into predictable profits while keeping clients happy and books balanced. The problem isn't just choosing between time & materials and fixed bid. It's