There is a reason for everything
Recently Dell refused a purchase order from me, because I had raised the quantity from 6 to 7 (and kept the same unit price). They had to send another quote, which for some reason had a lower price. So they should have accepted the first PO.
I do know why vendors ignore potential customers that call them (as opposed to the potential customers that they cold call). It is because sales people believe that the only reason you would call them is that you have bad credit with your current vendor.