What happens when your customers are willing to use your product, but they're not willing to pay for it? Answer: Your business model may be wrong. That's what Ilir Sela learned after launching Slice, a company that helps local pizzerias sell online. He found plenty of early customers, but they weren't paying their invoices. As he dug deeper, he realized the problem wasn't them -- it was him. And he began the long process of figuring out what (and how) people were willing to pay.