Then I think krm01 answer is the right path: "best way is to build a product for a single customer, who will pay you upfront". About it being B2C product, ther

Then I think krm01 answer is the right path: "best way is to build a product for a single customer, who will pay you upfront". About it being B2C product, there you have the exact reason why it is better to bootstrap B2B products than B2C. Building a B2B product is how you bootstrap a startup effectively. If building a B2C is "non-negotiable", then you should try to minimize the cost of building a product the most. For example, not coding a product. There is a new site that aims at this sort of solution: https://www.makerpad.co https://www.makerpad.co. Validating business without code. Might be useful.