One of the things I've learned from working with international clients is that the biggest challenges are rarely technical. Most of the time, they come from something much simpler: expectations that were never discussed.
When a client hires a firm in another country, they are not only dealing with a different legal or tax system. They are also dealing with a different business culture, different communication habits, and different assumptions about how professional services should be delivered.
This is where problems often begin.
I've seen situations where both sides believed everything was going well, only to discover weeks later that they had completely different expectations regarding timing, deliverables, or even the level of involvement expected from the advisor.