Not sure what you are referring to -- at least in the P/NP problem complexity classification verifying the solution is easy, coming up is P/NP-hard, i.e hard.

So if I gave you a flawless solution to a sudoku problem, would you tell me that it was harder for you to verify it than it was for the solution to be produced?

I had to do exactly this in a practical coding interview. Fun was had.

I think that really depends on the problem space. If I had to hire a sales team to increase revenue, then I hire them and check the revenue numbers (with basic accounting for other secondary variables), its pretty straight forward to validate.