It seems like you pay up front with cash and video making before and after new parts, then you get discounts from a few parts companies. The companies write off the discount as advertising, and the middleman keeps the first payment for their time and overhead.
I would prefer to have more of a choice for where I buy parts, but this could save you money in the long run if you buy a lot of parts from the companies listed and they keep giving you a discounted price.
“Banking institutions have banished precious metals and substituted a more fluctuating and unsafe medium; they have withdrawn capital from useful improvements and employments to nourish idleness for the few, who prefer demoralizing pursuits to labors useful to the whole; the peace of the whole is endangered by evils more easily to be deplored than remedied." by Thomas Jefferson,1810 (edited)