I don't invoice. I get credit cards before work lol
This. I won't do work unless I'm paid first or immediately afterwards. No free loans for my clients. They don't like it? Then go somewhere else for a free loan.
For large jobs ($20,000+), I'll invoice as I go along. But unless they want me to drop them like a hot potato in the middle of the job, they'll pay the invoice immediately. Just did a major job ($83,000) and they paid as we went along. I'd never expect an $83,000 payment up-front, but they paid $25,000 to start (my cost), an additional $35,000 when the job was halfway through, and the rest at job completion. It takes some companies off-guard that have never worked this way, but it's your business and you set the terms. If you allow them to abuse you, then don't blame them for taking advantage of you - you're allowing it.
I f*cking hate lawyers. I usually demand 100% of the job paid upfront before I start when I'm dealing with lawyers. I'll make exceptions for past clients on a case by case basis.
Medical facilities are also cheap as f*ck so I make sure to collect payment ASAP so they can't go back on what they've already agreed to. They also love Net 30/60/90 terms so I have to nip that in the bud right away when I'm working with a new medical client.
It's my job to fix computers, not give out loans and collect invoices. If they want a loan they can talk to a bank. I'm in the computer fixing business, not the banking business. I can either be a computer repair shop or a bank - I can't be both.