Sales is the key conversion metric for measuring how Amazon ad campaigns drive actual purchases and business growth.

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The correct answer is: Sales

Explanation: Sales is the primary metric you should use to measure your conversion goals in Amazon Ads campaigns. Tracking sales helps you directly assess how your ads are impacting customer purchases and indicates the effectiveness of your advertising in driving conversions. By monitoring sales, you can evaluate which strategies, ads, and targeting options produce the best results for your business objectives.