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.
“It is difficult to get a man to understand something, when his salary depends on his not understanding it.”
― by Upton Sinclair, who helped clean up the meat packing industry and other factories