Export the Sponsored Products Search Term report, filter to terms with zero orders, and sort by spend. Any term that has spent meaningfully more than your average cost-per-click without producing a single order is wasting money. Add those as negative exact keywords at the ad group level, and negate the obvious irrelevant patterns as negative phrase.
Set a defensible threshold
A term with 3 clicks and no orders proves nothing — that is normal variance. A term with 40 clicks and no orders is a statement.
A practical rule of thumb: give a term roughly 2–3× the number of clicks implied by your conversion rate before judging it. If you convert at 10%, expect a sale within about 10 clicks, so 25–30 clicks with nothing is a genuine signal.
Negative exact vs negative phrase
Negative exact blocks precisely that search term and nothing else. It is safe and surgical — use it for individual proven losers.
Negative phrase blocks anything containing that string. It is powerful and dangerous. Use it for whole categories of wrong intent, such as a competitor brand name or a modifier like 'free' or 'used', but check what else it would block first.
This is maintenance, not a project
New search terms appear continuously as Amazon tests matches. A negation pass done once decays within weeks. Doing it on a fixed weekly or fortnightly cadence is what keeps spend clean.
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