Google AdWords offers the following six types of ad extensions. They have the potential to complement a text ad with further information for potential customers. All ad extensions have in common that they do not impose any costs to the advertiser unless they are used by a potential customer.
A call extension enables a potential customer to call the advertiser. A phone number is displayed directly inside the advertisement.
A location extension is a means to inform the customer about the location of the advertiser’s store. This only makes sense for geographical targeting and if stores are available.
Offer extensions enable the advertiser to provide a link to a special offer on his website. This is very helpful for temporary offerings.
Sitelinks are links to certain parts of the advertiser’s website. Often advertisers link to subcategories of their site. A clothing store might link to men’s and women’s wear. Others link to subcategories of what the ad presents. This improves a user’s navigation experience.
Sitelinks are only visible for the 3 highest ranked ads.
Social annotations link the ad to the company’s Google+ account. The annotation informs about the number of followers and is a link to the Google+ page of the advertiser. This only works if the same account is used for the Google+ appearance and for AdWords.
Google collects user experience ratings for various retailers. These can optionally be displayed in the ad.