Many years ago, I and a buddy were hired to develop our very first website while still students. We had it done in two days or so because it was a simple site and we were excited to do the work.
We called the client on speakerphone so we could both hear what he said.
Me: The website is done, we can bring the CD tomorrow. We only accept payment in cash as per the contract, please have the money on hand. In the mean time we are setting up the hosting for you.
Client: That's great, deliver the file and I'll pay you in a couple weeks. I'm a bit short on cash right now.
My friend was shaking his head vigorously.
Me: No. We can wait for when you have the money and finalize it then. We're still setting up the hosting anyway, so if it will take you a week or two to arrange payment that's fine.
He hung up, and we never heard back.