I always assumed that the sales rep guesses a price point that you're willing to pay based on how big your company is (and of course building in the inevitable 20% discount your procurement team will want).
YMMV, but in my experience this is less common than you think and is instead more based on the baseline costs of specific features or customizations the client wants.
In other words, it’s rare to have a huge variation of costs given to customers for the same product, even if they are higher or lower for certain customers.
