Change orders that don't kill the margin
Scope creep is a pricing problem disguised as a customer-service problem.
Price every change in writing, before the work
A 60-second written change order (even a text with a number and a yes) protects the relationship and the margin. Verbal scope changes are unpaid work.
Don't 'just throw it in'
Every free favor trains the customer that extras are free. Charge a small change order fee even on small adds. It sets the precedent without breaking the relationship.
Track change orders as their own line
On any job over a few thousand dollars, separating change-order revenue from base scope reveals how much of your real margin lives there. For many shops, it's the entire profit.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.