Make sure your products are properly categorized by following our instructions on setting the Category ID (in this topic).
To keep CPC costs low, you can use the Product Exclusion Criteria to filter out non-performing items, or items under a certain price. As an example, you can filter out a product if it does not yield any sales within 50 clicks.
Review the Shopping.com data feed specifications, and submit any additional attributes as recommended by them.
Recommended Attributes for Optimization, Source: Shopping.com
For Shopping.com categorization, we recommend that you add a field to your Yahoo Store called "shopping-category-id". Then, populate it with the appropriate category from the Shopping.com Taxonomy. You should select the single Category ID of the most specific category that applies to the product. For example, you would enter "419" for a telephone, which would place it in the "Electronics > Communications > Phones" sub-category.
Our shopping.com template is already configured to map this field from your Yahoo Store, otherwise, you can change the field name by going to "Manage > Define Fields". The automatic/manual categorization provided in your Shopping.com merchant account is usually not as reliable as this method.
Shopping.com displays prices based on the location that is entered by the user browsing the site (signed-in or not). In some states, the price may include sales tax, and shipping may be calculated based on the user's location.
After adding or removing fields in you Shopping.com data feed, you must remap the columns in your Shopping.com Merchant Account in order for them to recognize the changes. This is very simple to do. Just follow the step-by-step instructions below.
Reference: How do I map my column headers? in Shopping.com Merchant Support.