I've bought direct but not from that mill. It was very good quality carpet.

Go to a liquidation center

You can't buy them in bulk--at least we didn't find them in bulk, but you can get decent one through Amazon.com.

Each business will have their own overhead and profit structure that goes into calculating their needed margins on products. The industry runs on margins, not markup. Everyone will have a different %. There is no industry standard, and it is confidential information for each business. You can ask, but don't expect to get answers unless you are willing to share your job's compensation and year end tax results with them.