In no order/priority: strength of management (particularly those that will stay), customer concentration, related party transactions, confidential survey of key customers, defensible assumptions for their 3 year go forward plan, how often they competitively quote all vendors, QE, environmental issues, customer history (years), core competencies (vis a vis competitors), legal and regulatory issues, remaining life of IP, what are the owner's KPI (their dashboard), trends in gpm% and why its changes, for starters. Agree with Joseph: you can hire investigative services to trace, profile the key players.

This is so helpful! Thank you so much for this. If you feel like there's anything you want to add later or anyone else you think would have good advice, please feel free to come back to this post!!