How would you know if their stated runway is realistic? What I mean, I feel that startup is gonna try to get you no matter what (in some cases), so how do you know if they are telling truth or not?
Of course, you can never know for sure if someone is telling the truth or not, but they way they defend their answer says a lot in my opinion. People who tend to lie usually don't like getting into the numbers, and people who are honest about runway tend to pay pretty close attention to them.
If they don't wanna show you the business data, then, that's not somewhere where you should work.
If you don't trust that they are actually using accurate data, the business will definitely fail and you shouldn't work there.