I'm interested in the space of IT consultancies / tech consultancies / digital agencies. Basically, firms that do tech services for clients, ranging anywhere from building websites to integrating CRMs / ERPs / etc to building much more complex solutions.

There's one I've found that has promising financials. I'm very aware of the risk that the consultancy rests on the founder's or the founder + management team's shoulders - ie a lot of key person risk. What I've heard in initial conversations has mitigated my concerns a bit, but of course I'd like to solidify my understanding there even more.

What are some good diligence questions to ask for companies in this space, about the above topic or in general?