On October 1st Microsoft released an update to the quality-based ranking system in adCenter. This is the formula that dictates which ads appear in the “Mainline” above the natural listings.
“With these changes, the marketplace is now more dynamic, and any ad with a Quality Based Ranking above the mainline threshold may appear in the mainline”
Advertisers can now easily control whether their ads appear in the “mainline” by improving the Click Through Rate (CTR), or increasing the Max Bid.
If y0u want to improve your ad quality Microsoft suggest you check your adcenter account regularly, and adjust your ad copy, bid price and other key attributes. Remember to test different ad variations to determine which delivers a higher CTR and run with it!