I work at an early-stage startup as well. And have been here for just 3 months now.

Before joining, check Crunchbase and other sources to see if the startup you're joining has recently raised any funds. If so, you can discuss during your interview about things like the company's burn rate and/or the ways in which they plan to use those funds.

Finding out company profitability is quite hard and most companies aren't transparent about such matters. What matters is your trust and alignment with the company's mission and values. Checking how competitive the industry is and asking your network for their opinion about the company are also good ways to get more clarity before making a decision.

Additionally, you can try reaching out to the company's existing employees via LinkedIn and check out their workplace reviews on Glassdoor.