Professionally, this is something close to the workhorse of the knowledge economy. A Virgo Mercury is at its best wherever people are paid for accuracy, checking and good systems: editing and proofreading, data analysis, accounting and audit, programming — code review and testing especially — technical documentation, medical diagnostics, legal work with contracts, quality control on a production line. Anything, in short, where the job is to catch the error before a client or a regulator does.
The roles that suit them best are the ones where they become a team's "second layer of checking": chief editor, technical lead, senior analyst, consulting auditor. Colleagues quickly come to rely on it — if this person has looked something over and signed it off, it can go to the customer. That reputation builds slowly, but once it's there it tends to work in their favour for decades rather than months.
In teaching, this placement is strong in exact subjects with a checkable result — maths, languages at the level of grammar, programming, bookkeeping, medical diagnostics. It tends to do less well with subjects that ask you to inspire and fire up a room; other placements carry that load more easily.
One thing I notice often is how much people with this Mercury undersell themselves at work. They assume they're just doing the job to a normal standard, and they don't quite grasp that, for most people, "normal" means a fair bit less precision than this. As a result they rarely push their own case, and not infrequently get stuck on rungs below their actual level. Working deliberately on being visible — talking about results, writing the work up, speaking at professional events — isn't marketing fluff for this placement; it's the way out of being an invisible expert. When it clicks, careers tend to take a step up: it isn't only colleagues who start to notice them, but the wider market too. Treat all of this as a way to recognise your own patterns and have a bit of fun with them, not as a forecast of what's bound to happen.