I recently purchased a new home that I need to do major work on (new plumbing, electric, HVAC, etc).

In any event, even if the unforeseen monster does pop up (plumbing problem, foundation, mold etc) etc. 

You are probably better just negotiating with a plumbing supply company or big box store.

I've been reading my city's code book, but are there any other methods to learn code in a specific area other than just reading the code book?

There may also be underground wiring and plumbing that should be removed as well...

Compare it with the enemy method for accurate assessment 

I backed out of a few deals even after realtors found buyers for my properties and I never felt bad for my realtor because my realtors have the choice of understanding that people back out and the realtors can cut me off for life, or be nice about my backing out and get more business in the future.I am also a plumbing contractor and we do a large volume of business where my employees sign contracts with our customers, work on my customers homes for several hours and sometimes even a full day.

That applies to the Brrr method.

I have tried many other things, but those tried and true methods will make the phone ring. 

I am learning about this method right now using David Greene's book.