TL;DR: Price negotiation between buy-side and sell-side agents works through a structured exchange of proposals, not a single auction event. The buy-side agent carries a CPM range from its mandate; the sell-side agent carries a CPM floor from the publisher's parameters. Both agents evaluate whether agreement is possible within those ranges, and if it is, the agreed price is written to the bilateral DealSheet. If it is not, either party can counter-propose or decline.

How agents negotiate prices is one of the most frequently misunderstood aspects of agent-to-agent advertising. The instinctive comparison is with a real-time bidding auction, where a buyer submits a bid and the highest bid wins. Agent-to-agent price negotiation does not work this way. It is bilateral and iterative, not competitive and simultaneous.

How the CPM range works on the buy side

A buy-side agent's mandate defines the CPM parameters within which the agent can operate. This typically takes the form of a range: a maximum CPM the agent is authorised to agree to for a given inventory category, and a target CPM below which the agent should aim to negotiate. These parameters are set by the buyer's trading desk when the mandate is written, based on the campaign's goals and the buyer's historical data on fair value for the relevant inventory.

When the buy-side agent initiates a deal proposal, it does not immediately offer the maximum CPM. It proposes a CPM within its authorised range, typically closer to the target than the maximum, to preserve negotiating room for a counterproposal.

The mandate may also specify different CPM ranges for different inventory categories. Premium contextual inventory may have a higher authorised ceiling than standard run-of-network inventory. The agent applies the relevant range based on the inventory parameters in the proposal it is evaluating.

How the CPM floor works on the sell side

The publisher's sell-side agent operates under an equivalent mandate that defines the CPM floor below which the agent cannot accept a deal. The floor is set by the publisher and may vary by inventory category, buyer category, audience segment, or time of day.

When the sell-side agent receives a buy-side proposal, it compares the proposed CPM against the applicable floor. If the proposed CPM is at or above the floor, the proposal is within the publisher's acceptable range. If it is below the floor, the sell-side agent has two options: decline the proposal, or counter-propose at the floor or at a price point above the floor that it is authorised to offer.

The sell-side agent cannot accept a price below its mandate floor without triggering a human approval request. This is the governance boundary: the agent can negotiate autonomously within its mandate, but cannot override the publisher's pricing decisions.

How the negotiation converges

If the buy-side agent's initial proposal is below the sell-side agent's floor, the sell-side agent sends a counterproposal at or above the floor. The buy-side agent evaluates the counterproposal against its mandate ceiling. If the counterproposal is within the buy-side mandate range, the buy-side agent can accept. If it is above the buy-side mandate ceiling, the buy-side agent can either counter-propose at its ceiling or decline.

Negotiation converges when one party's proposal falls within the other party's mandate range. At that point, the accepting party's agent signals agreement, and the agreed price is written to the DealSheet along with all other agreed terms.

Negotiation fails to converge when neither party can reach a price that falls within both mandate ranges. In this case, the agents decline and the deal is not made. No human involvement is required for a failed negotiation: the agents determine autonomously that agreement is not achievable on current terms.

What determines the final price

The final agreed price is determined by the overlap between the two parties' mandate ranges, and by which party is willing to move first. An agent that counter-proposes early concedes price information to the counterparty. An agent that holds its position forces the counterparty to reveal whether they are willing to move.

This is structurally similar to human bilateral negotiation. The difference is speed: agent negotiation cycles complete in seconds, allowing a buy-side agent to run multiple parallel negotiations with different sell-side agents and compare the agreed prices across publishers.

The mandate parameters are therefore the key determinant of price outcomes. A buyer whose mandate is well-calibrated to market conditions, with a realistic target CPM and a ceiling that reflects the maximum value the inventory provides, will get good price outcomes. A buyer whose mandate ceiling is set too high will overpay whenever the sell-side agent has no floor pressure to move to a lower price. A buyer whose mandate is set too low will fail to reach agreement on inventory that would have been good value at a slightly higher CPM.

Mandate calibration is a trading skill. The agents execute the negotiation; the humans define the parameters that determine the outcome.