We once sold contracts on eBay. There, we were successful in maintaining 100% Positive Feedback.
During the 2month period we sold over 175 contracts, using three miners. In order to make this possible we developed a system that automated the scheduling of the mining rigs.
The process also allowed us to grow and use independent miner operators from around the world. Allowing us to service a greater number of contracts, at very competitive pricing.
http://808Mining.com/Blank.php shows the current prices.