Okay, but having them solve coding problems on the whiteboard doesn't provide any evidence of that either.

If they say they delivered projects on time with "great maintainable code," ask them what makes code maintainable, have them provide examples (using pseudocode) and talk through each one. Ask them about a time when they had to sacrifice maintainability for time, application performance or user experience. Ask them what they learned from the ordeal.

In my opinion you're going to be much more likely to accurately judge their expertise level based on their answers to such questions. The reason is simple: one can memorize whiteboard questions prior to the interview. They can't, however, bullshit their way through questions that are experience-based - and if they do, well, you should hire them immediately because you just found yourself a great salesperson!