Tips on Buying Cars: buying new car, sound counsel, holdback

Question
I'm about to buy a new Buick. I've been told by friends, to negotiate a price that is "close to center line invoice" or 1% over.
Is that sound counsel? and what is a "center line invoice? how many "invoices" are ther per car?

Answer
There is only one actual invoice for a new car.  That is the amount the dealer pays for the vehicle.  This invoice includes holdback, which is refunded to the dealer, advertising allowance(in some cases) which is either rebated to the dealer or given to a local dealer association for advertising.  There may be rebates, financing programs or cash back to the dealer.  The best way to find these programs and also see what most people are paying for the vehicle is to go to:
www.edmunds.com
They have all the figures.  Best of luck to you.  Bud