An advertiser makes edits to an ad and notices that its position is then lower than that of the previous version. What’s the most likely cause?
The advertiser’s landing page is down for maintenance
The edited ad is less relevant to the keywords in the ad group
The advertiser’s budget has been depleted
The edited ad has a lower conversion rate
Ad position is determined by a formula called Ad Rank that gives your ad a score based on your bid, the quality of your ads and landing page, and the expected impact of extensions and other ad formats. So even if your competition bids more than you, you can still win a higher position — at a lower price — with highly relevant keywords and ads.
You can read more here: https://support.google.com/partners/answer/6300?hl=en