Great topic, a lot depends on the product or service you are providing. When I sold handmade wedding invitations, I only needed to make 1 or 2 samples and then I would get paid 50% of the total before the rest were made. So the product was actually financed by the buyer.
There is a whole software making business that is run by a guy named Dane Maxwell where the development of his products are fully paid for in advance by 1 or 2 clients and he offers them free lifetime updates or some other bonus. It was a very interesting concept, I heard him on a podcast called smart passive income by Pat Flynn, it was episode 46. I have no affiliation with either of those guys, but it certainly addressed cash flow in a new way.
I have heard a lot about crowd sourcing products before they are made also, but have no personal experience with that. I think there is a lot of room for creativity in this topic of cash flow and am interested to hear others inpur