I think the "real world, open-book" problems have to be crafted well, but I think they give a good sense of "Common sense". They are set up that you can absolut

I think the "real world, open-book" problems have to be crafted well, but I think they give a good sense of "Common sense". They are set up that you can absolutely prematurely optimize or go down really crazy paths (and I've seen them happen). You don't need another developer to pair program to get that - essentially you set up a clean computer with their editor on it and your testing/interview environment, and they can hack away while you watch. But yes, if there's some way to get a candidate to pair program on actual, real code with real developers, it's invaluable. Just make sure they sign a contract stating they are giving you the rights to the code, and that they are adequately compensated for their time at some reasonable hourly rate.