“Can this startup be marketed profitably?”
“Can the profitable marketing scale?”
Of course you can’t definitively answer these questions until you try marketing the product. But, if you aren’t pretty confident that the answer to these questions is yes, you shouldn’t launch the business. Too many people start trying to build a product and believe they’ll figure out the marketing piece later. Some get lucky, but the majority fail.
If you start your business with these questions in mind, you are much more likely to build a successful business.