You can run Amazon PPC yourself, and at low spend you probably should — the work is mostly disciplined weekly maintenance rather than secret knowledge. An agency becomes worth its fee when spend is high enough that a few points of ACOS exceed the retainer, or when the weekly cadence is not happening because nobody has time for it.
The honest arithmetic
If you spend $3,000 a month on ads, a 5-point ACOS improvement is worth roughly $150 a month, which does not cover a retainer. At $30,000 a month the same improvement is worth $1,500 and the maths changes.
Any agency unwilling to walk you through this calculation before quoting is not worth hiring.
What to check before signing
Ask what specifically will be done each week, what reporting looks like, whether you keep the campaign structure and keyword lists if you leave, and whether the contract is month-to-month after an initial period.
Be sceptical of guaranteed rank or guaranteed sales figures. Nobody controls Amazon's algorithm or your competitors' budgets.
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