Google Shopping Custom Labels for Adwords is a helpful attribute that allows you to define your campaigns at a much higher level.
|Item ID||custom label 0||custom label 1||custom label 2||custom label 3||custom label 4|
Using custom labels allows you to break away from the constraints within categories, product types, etc…
You are limited to a total of 1000 different values. This means that you can use any different word or sentence in any of the 5 custom label columns. Each unique value in these 5 columns will be counted as 1.
If we look at the table below, we can see that we have 9 cells, but we only have 6 different values. Any value can be in any column, as long as the total for all 5 columns does not exceed 1000 unique values.
You can start by using your top-level Custom Label 0 than define it to a subdivision using categories, product type, brand, product id etc…
Or you can start with the top-level category than use custom labels down the tree, the combinations are limitless and allow you to define your product grouping in a very effective way.
Here is a guide on how to create product group subdivisions.
If you have a lot of products, than creating multiple ad groups per product listing will allow you to see searched keywords for that particular group. This allows you to better control your negative keywords.
So for example I have two groups, Coffee and Juice. When I go inside dimension and select view searched keywords, I can use the filter option to change the results for a specified group.