Bids and Dynamic Bidding

Your bid is the most you will pay per click, and dynamic bidding lets Amazon adjust that bid in real time by how likely a sale is.

You set a cost-per-click bid, then choose a rule. Fixed keeps the bid steady, down-only lowers it when a conversion looks unlikely, and up-and-down both raises it for likely conversions, by as much as 100 percent, and lowers it otherwise.

You bid on "insulated water bottle" with down-only. On a search Amazon reads as unlikely to convert, it quietly drops your effective bid, so you pay less on weak auctions and hold the full bid on strong ones.

Up-and-down can double your click cost. On top of search it can raise the bid by as much as 100 percent, so ACoS spikes if you switch it on before you know a keyword converts; start down-only and move up once the data is there.

The bid is a ceiling, not a promise.