Automatic Targeting of Competitor Products ASINs
Automatic campaigns will have Amazon target any page that seems relevant to your product:
This mainly means either the search results pages, or the listing pages of other similar products:
These kinds of ads are generated automatically in automatic campagins, as well as manually through manual product targeting campaigns.
Target "Positive" ASINs and their Top Keywords
Amazon introduced Product Targeting in November 2018, so that you can actively target well working ASINs in a manual campaign. Additionally, you can make use of the respective ASIN's keywords by
a) checking the keywords in the product's title or
b) checking Sonar's Reverse ASIN lookup. Sonar will display the keywords for which the respective ASIN is ranking on the first searchresult pages.
When placing ads for the respective keywords from Sonar, you can make potential customers aware of your product even before the competitor ASIN is found.
Adding Negative ASINs (Manual Campaigns only)
In your manual product targeting (category) campaigns, you can add negative ASINs to avoid running ads on these products:
Additionally, as described above for well working ASINs, the keywords of badly working ASINs could be set to negative.
Although technically ASINs can also be added to your automatic adgroups' negative targets, this does not have any effect. It only prevents the ad from being shown if somebody happens to enter that ASIN into Amazon's search bar.