2 cents
I think many, if not most regulars, on this forum are often referred to a "Guru" in their own local circles. People at work call me a "Guru", but I know better.
For me this is a hobby, tangentially related to my job. That said, when an Excel VBA question does come up at work, I am the person everyone comes to. So don't take what I say as the advice of an Expert.
Excel/VBA covers a very wide spectrum. There are certain skills that should be common to all VBA programmers, which others will hopefully spaeak about. I think you need to think about what specific tasks you will be asking your programmer to perform.
Will they be working with Databases? Access? SQL? User Interfaces/ Userforms? Will the run simulations? Finanancial calculations? Will they need to create add-ins/ programs for hundreds of other users? What is it you would like them to do?
Most "Gurus" will ACE an Excel or simple VBA test.
At an interview I'd present a handful of problems (real or representative of what you'd like them to be able to do), and ask them how they would approach the problem. If they know their stuff, I believe they should be able to outline a potential solution and explain the advantages and disadvantages of their approach.
Ask for specific examples of problems that the programmer has solved. Ask about difficulties encountered, solutions considered etc.
I also think a good programmer knows what they are good at, and what they do not have as much experience working with. You could ask about strengths and weaknesses.
Hopefully those far more familiar with Excel/VBA development will chime in.
