We have created a similar setup to AdWords for the performance aftermarket.
We look at Google for features and functionality for our product roadmap.
Google uses variables in their results that will drive you crazy. You can be in positions one, two or three in simultaneous searches from three computers. That's on the organic results. On the paid results, you will also be rotated for no apparent reason, but advertisers now have control over dayparts, regionality and other aspects of AdWords that makes it very hard to get a consistent result. It's further complicated by distributed serving -- so that Google may have eight servers responding to searches and all giving slightly different results.
People have made
SEO/SEM a full-time job for this reason.