Several years ago when I worked for a friend we dicovered a basic truth:  Screw ups begat screw ups.  Especially when dealing with customers.  If something goes wrong it just seems to cascade.  One problem after another after another.

That's a polite way of saying stuff runs downhill and picks up speed as it goes.

Go talk to them because there are several issues going on here.  I am assuming the salesman is aware of your prior relationship?  And he is behaving like this with someone he KNOWS has an in to his boss?

Confirmed: Salesman is an idiot.

They need to know the way this salesman is treating customers. He can kill their business with just a few cases like this where the customer isn't as considerate as you are.

As for the building, "I'm sorry, but that is not what I ordered and I will not accept it."  If it costs the company several thousand dollars to educate a salesman on how to listen to a customer it is not your fault.

Lay everything out for them:  The concrete engineer messed up.  The building design was messed up.  You are now questioning whether or not several of your specifications and requirements have been followed.  THEY have to do something and YOU are not accepting a building you didn't order.

Be calm and freindly, but don't budge.  Because as you said, you are the one looking at it every day.