There are a number of critical questions you need to answer about your market:

Does your business idea really meet a compelling, unfulfilled market need?  You may think so, but do your target customers? 

How big is the target market?  Is it large enough to meet your revenue goals?  Is it large enough to be attractive to investors?

What segments are there to your target market?  Which one will you tackle first, and why?

What is your sustainable competitive advange that leads you to think you can win over the competition?

If the need is real, how much will customers pay?  How do you know they'll pay that much?  At that price, can you make enough money to make the business work?