On Google Shopping, you can’t bid for specific search queries. Instead, you can use negative keywords to filter out what you don’t want your ads to show up for.
When you submit your product feed to Merchant Center, Google crawls this information to identify search queries. However, negative keywords give you greater control over which search queries your ads will show up for.
From your Search terms report in your Shopping campaigns, you can see which search queries are triggering your ad. From there, you can determine which search queries you’d rather not show up for. For example, you may be showing up for queries that are totally irrelevant to your ad, which will lead to a low CTR, or for which you may be spending money on clicks which don’t lead to sales.