Deposits and milestone payments without losing the job
If you're funding your customer's project out of your own cash, you have a deposit policy problem.
State it as standard, not a request
'Our standard schedule is a deposit at signing, a draw at material delivery, and the balance at completion.' Said calmly, almost nobody pushes back.
Size the deposit to your real exposure
A small job needs a small deposit. A custom-order or long-lead-time job needs enough deposit to cover the materials. Anchor the number to the cost, not a percentage.
Get it in writing every time
A signed proposal with the payment schedule on it is the difference between getting paid and chasing money. Verbal payment plans are the leading cause of bad receivables.
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.