What factors would you consider when evaluating a job offer from an early stage startup?

Someone close to me got an offer from an early stage startup (under 20 employees) recently and asked me if the offer is good (I work at a pre-IPO company). We discussed the basic factors of whether they like the team, their role, the numbers and whether they believe in the product and the founders. Given the early stage of the startup, the risk is higher and there is a general lack of external signals to assess the opportunity. So, I thought of reaching out to the wisdom of the HN crowd to see what other factors should one consider in deciding whether to bet the next few years of their career on a startup.