...the discounted rates they negotiate for services...
Back in the day, I was with a engineering firm doing work for Enron. Our company made a mistake when we requested a quotation for several very large valves on a gas pipeline job. We sent the paperwork out in our name. We did not make clear the purchaser was going to be Enron, who was a major buyer of these valves and had pre-negotiated rates on different sizes and ratings.
When the mistake was noticed, we sent the RFQ out again making clear it was Enron buying. The quote came back 10% higher for Enron than the basic off-the-street pricing.
This was something like $75~85k each for a couple dozen. It made quite a difference.