I am glad that you brought this up as another to supplementing start-up cash. I still do this to a degree by selling collectables on Amazon. I don’t have big store and I only really sell every now and again. However, anything i’ve sold and shipped I bought so long ago that $100 is $100 I didn’t have today. Another way to complementing a business start up is reaching out to co-founders or “a shark tank” of people that might be willing to dive in for a piece of the pie as it grows. This is known as sweat equity that only takes time and effort rather than money investments. You may have a great idea and others might agree with you and be willing to put in some work to make it real.