When buying tile/granite/slate, are there different types of contractor discounts?

I wanted to buy some cermaic tiles from this place and the lady said that if get my contractor to buy it, that they could sell it cheaper. I asked how much cheaper and she said it depends on what kind/type of contracting license they have. Is this true? do some contracting license get more discounts than others? if so what type gets the BEST discounts?