Ignore the beat-down by self righteous contractors-- here is how I got
the deal--FWIW.

I was replacing my roof, and called the local roofing supply company
to get a price--- I described what I wanted using general terms, they
gave me a price. I wrote down the price and model number and other
descriptions. Later, I decided to get the supplies from another
location, same company. I called them to confirm I would get the same
price, but instead of sounding like a dolt-do-it-yourselfer,
describing in general terms what I wanted, I just said (somethign
like) "I need 14 square of GAF shingles... " and went on to refer to
it using item number, etc. I found the price quoted was about 20%
less. I thought about it for a while, and figured out that they had
given me what I presume was a contractors discount, just because I
sounded like one. The next time I needed some stuff I tried the same
thing, getting the insiders model numbers from one location, then
going into another location, in my work clothes, and asking for stuff
by model number, etc.. and I got a better price. Go figure, not sure
if it works anywhere else, but for this particular store it appeared
to be an informal system, and if you looked and sounded like a
contractor you got a better price... give it your best shot.

Save your flames, if they guy didn't ask if I was a contractor, and
just assumed I was, that is on him, not me. I am not going to correct
him and ask him to raise the prices. Also, if the business relies on
this informal method of setting prices, TOUGH!