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Even if the service center is not a profit center, it is going to have much larger fixed (facility, utilities, insurance, etc) and operating (salaries, inventory) costs to operate than a warehouse with a web store front. To expect Tesla to be able to sell parts at the SC for the same price as what you could do for an equivalent part on-line or from a specialty retailer is a little unrealistic. The service center isn't a charity, they still have to recoup their costs (all of them, not just the purchase cost of the part from the supplier).