In my experience the vast majority of businesses will not entertain the idea of cash up front, period. I bet that you wouldn't either. If you were building a house, and the builder demanded cash up front, you'd laugh in his face.
Finding good clients is important, but if you demand to be paid in advance, get used to waiting those tables because you're going to be doing it a long time. Note: you will not be paid in advance for waiting those tables, either.
If you’re doing work for clients upfront without a deposit, you are taking a huge risk. Which is probably why out of more than $2 million billed, I’ve only had a single client not pay me, and that was a startup that went under completely.
Then the time-tracking component would strongly warn against commencing work until the invoice was paid, etc.
So, basically, a very opinionated business framework web app.
That's how a lot of builders work - if you're having a custom built home, you're going to need to put down a deposit.
It basically happens in real time, but a weekly check is still tolerable compared to net-60.
If they don't take those terms, then they don't get your services.
If that means you have to wait tables until you find a few legit clients, then so be it.