I recently had some work done by an electrician. It was permitted and inspected. The inspector merely looked to see that it had been done by a licensed electrician. I inspected and found several problems, which he ended up fixing (he wanted to be paid, after all). I know several people in the trades who say this is very common.
Building code doesn't accomplish half of what it's supposed to, but somehow manages to cost a lot more than it's supposed to.
A true craftsman would always do the job perfectly, but subcontractors are often unsupervised, inexperienced, and rushing from job to job.
As a result of my remodeling misadventures, I've had to learn stuff like electrical. I bought every remodeling book. Filled with conflicting advice.
I barely know enough to know what questions to ask. Further, I don't want to know enough to form my own opinion. Instead, I have the building codes.
Installing a sink? Do it like this. Boom, done. It's been a fantastic resource.