Having been both the interviewer and the candidate in this kind of situation, this is really a big interviewer training failure.

The general way to handle this as an interviewer is really simple: acknowledge that the interviewee gave a good answer, but ask that for the purposes of evaluating their technical design skills that you'd like for them to design a new system/code a new implementation to solve this problem.

If the candidate isn't willing to suspend disbelief for the exercise, then you can consider that alongside all of the other signals your interviewer team gets about the candidate. I generally take it as a negative signal, not because I need conformance, but because I need someone who can work through honest technical disagreements.

As a candidate, what's worked for me before was to ask the interviewer if they'd prefer that I pretend ____ doesn't exist and come up with a new design, but it makes me question whether I want to join that team. IMO it's the systems design equivalent of the interviewer arguing with you about your valid algorithm because it's not the one the interviewer expects.

A good interviewer won’t be looking for a single solution to the problem. I’d expect them to entertain the Google Sheets answer - it’s good signal that the candidate will consider what already exists in the world. I’d rather extend the problem: the team is spending considerable time iterating with manual entry, what would you do?

While I agree, how much training does anyone get as an interviewer? I spent 10+ years doing interviews at all sorts of orgs (including Fortune 500s, government, etc.) without a single hour of interviewer training.

Now that I think about it, none of those organizations ever trained me at anything at all. Huh.

I prefer pushing the constraints to motivate a different solution instead of asking them to do an unmotivated exercise.

“Google Sheets is a great solution for two people, but let’s say the department expands and now it’s ten people. How does this change your answer?”

It’s easy to break Google Sheets as a workflow by increasing the number of users, adding complex business logic, etc.

It’s interesting to see what candidates come up with and how they think. Sometimes the solutions are genuinely interesting. Mostly they’re not, which is okay. If you don’t give yourself the opportunity to learn as an interviewer, you’re missing out.

If I would be the interviewer in this kind of situation, I would just follow up with something like this: "that might be a good option, but let's assume you need to build a tool to replace those excel sheets, ..."

“Yeah okay forget sense, show me how good you are at budget protecting overdesign”