Insurance, wages and resources are just a few of the factors you haven't considered.
If you want a lower rate than someone else, just because you are "in the know" or come more often, why should you?
If you buy an item from the same shop everyday, should you get a discount?
I did take those items in to consideration hence my comment about my friends and jo-public and the pros'/cons argument, I used to have endless battles with people in my showrooms when I ran a couple of Volvo dealerships about the prices of my technicians, on how they are paying for a service, their training, guaranteed work, lighting, wages, the building they are standing in and so on.
And I am a believer that you should earn your discounts. I always buy paint from the site im playing at and don’t bring my own as I believe you should support and pay your way and help the site. But why let me pay £25 one day and then the day after when I bring four people all spending money at full prices (That wouldn’t be if I had not bought them along) make me pay £120.