[bmj]

if you hiring a house builder u would not ask him what a brick looks like right?

The problem with this is that a home builder/contractor will have a long list of references, and possibly examples of her work available for examination. Many engineers search for jobs while still employed, so they generally don't include as references co-workers and current managers. Further, if your employer doesn't allow you to open source your work, then you need to do open side projects to have any sort of real resume prospective employers can examine (and this is problematic since your day job may already take more than 40 hours of your time).

So, no, I don't need to ask a contractor if he knows what a brick looks like, but I do need to look at his references, look him on Angie's List, post to local message boards about his work. And, of course, I'm not an expert on home building, so it would be unreasonable to ask him questions about carpentry or framing.