It's possible. I like to think that magic is everywhere.
Perhaps just don't try to purchase anything if he gives you gold, unless you don't mind it disappearing from the till down the line. Of course, I don't think Muggles use gold for currency anyway, so it might not be an option.
It sounds as if you're determined to find out, so I wish you luck and only encourage you to use caution.
I don't think you can learn the type of magic I use, but I'm happy to continue in my criminal activities of teaching you about it. And it's possible you could actually learn other types of magic that people here practice. There's a lot of it.