They should be able to answer in a fair amount of detail what their runway looks like (i.e. cash in the bank, burn rate, projected hiring figures, etc.)

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.