How does google decide which ad is shown where?
Ad rank refers to the position your ad occupies on the results page of a given paid search.
High quality ratings will help you achieve better ad position at lower prices, as Google prefers content that is highly important to consumer queries.
Advertiser need to bid the minimum amount to be in a particular spot. You can’t bid 10 cents for example, and rank first for a $2-cost term. Ad rank thresholds on unique keywords mean your bid amount may be the deciding factor, and more important than the factors below, depending on the nature of the search.
Click through rate, relevance of ad text, landing page experience are the key factor which decides ad quality