If someone knows that much git, I'd hire them regardless. I'm so sick of untangling other peoples failed merges or trying to explain what the "not a fast-forward" issue means when their push fails.
It is fair to expect a developer to invest sometime in learning their tools well but git is a different beast. I know it solves a very complex problem but the fact that it exposes a complex interface to the user to do so seems like a shortcoming of the tool to me.
Heck, we even have a comic for it that shows how sometimes just saving my work, deleting my clone, re-cloning the repo and applying the changes in my work is easier than understanding the Git error messages: https://xkcd.com/1597/.
The tooltip in the comic is also sound advice: If that doesn't fix it, git.txt contains the phone number of a friend of mine who understands git. Just wait through a few minutes of 'It's really pretty simple, just think of branches as...' and eventually you'll learn the commands that will fix everything.
Compared to something like Rails, iOS development, or React + Redux + Redux Saga, Git is just a couple of commands and basic concepts. Everything is listed here, and I don't think that's an unreasonable number of commands to know: https://git-scm.com/docs
Either Git has a complex user interface like I claim or I am beginning to grow old.
I disagree. Like everyone, I've experienced a failed merge that turns into a diff nightmare. However, when it has happened I've figured out how to solve it myself instead of wasting someone else's time with it, and it hasn't happened in years now leading me to believe it is directly correlated with git skill-level.
Same for regular expressions. Once you know the syntax, they're pretty easy to understand. It just takes practice.