I always ask about the sales team - How many are there, how many years experience does the manager have in this sector, what's the experience of account execs, do they use BDRs, are they meeting sales goals.
Then, further, how does the sales team interact with engineering. How does customer feedback come back to engineering features, who demos, etc.
It doesn't matter if the engineering is top notch and there's no one to sell it. To me, if a company is past series A and the number of engineers is more than the number of sales employees, that's a warning sign.