When running product search campaigns in Google Shopping Ads, Google recommends that you work with different types of Comparison Shopping Service (CSS) partners to maximize opportunities. There are different types of CSS partners, offering both "self-service" and "full-service" models.
Self-Service CSS - A "self-service" CSS partner allows you to migrate your existing campaign from Google Shopping to take advantage of cheaper CPCs, although the support you receive may be limited. In addition to your direct campaign (managed internally or by an agency), a self-service CSS provider will go into the auctions on your behalf to provide you with greater reach. This will bring your shopping ads more visibility, clicks and sales.
Full-Service CSS - A full-service CSS partner will fully manage separate campaigns running parallel to your direct campaigns extending your reach to more search shoppers. In these separate campaigns the CSS will take care of auction bidding for you, optimizing bidding strategies to achieve your goals and ensuring the parallel campaigns do not compete against your direct campaigns. Some full-service CSS providers will use Google automation tools like Smart Bidding or Smart Shopping. Others, like Connexity, use their own homegrown bidding tools.