Mark was (is) talking about pricing a lumber yard quotes a repeat customer. You're dealing with (it seems) a manufacturer of aluminum decking, for the first and possibly only time.
Completely different animals.
For the record, I was pro asking for a better price. But if someone dropped the quote 8% and said I should have asked for a discount, I'd pocket the eight and ask for more.
That was round one.
Move onto round two.