Use negative keywords appropriately across your campaigns. 

Pilothouse Senior Amazon Media Buyer Clifford Donovan points out an example of how you can waste a lot of money on ads showing for the wrong keyword. 

Don’t do this 👇👇

Weber naturals is running a sponsored brand ad for Vitamin C, but it’s showing on the keyword "vitamin e gummies" (among many other irrelevant words). 

This is likely matching a phrase or broad match of "vitamin gummies.”  

Effective use of negative keywords can eliminate wasteful ad spend like this, bringing up ROAS.