First you did the right thing with the undercharge in the addition, second, I would no under no circumstances pay for that unit until it was safely on the dealers lot and I had a chance to inspect what I was buying. What are you going to do if is was made in the wrong color or lacking items you exected that should have been there. What if the transport company side swiped a sign post and only scratched the entire side? What if the ceiling shows water stains or some other possible problem. How are you going to walk away from a defective unit you now already own, good or bad? I think this is a bad idea no matter how I look at it for you.