TL;DR: A sell-side agent mandate is the publisher's equivalent of a buyer's media buying mandate. It defines what the sell-side agent is authorised to offer, the CPM floors it can accept, the deal types it can complete without human escalation, and the conditions under which it must stop or seek approval. A well-written sell-side mandate is the prerequisite for productive bilateral negotiation: without it, the sell-side agent either rejects every proposal that falls outside a narrow specification or accepts deals the publisher would not have approved.
Most of the discussion about mandates in agentic advertising focuses on the buy side. This is understandable: buyers are the active party in most deal negotiations, and the buy-side mandate is the document that defines what an agent is authorised to spend. But the sell-side mandate is equally important for the quality of bilateral negotiation.
A sell-side agent negotiating without a well-defined mandate is operating on defaults. It may accept or decline proposals based on floor price alone, without considering the full value of the deal to the publisher. It may accept low-CPM deals that meet the floor but represent poor yield for the publisher's best inventory. Or it may decline proposals that a human yield manager would have accepted because the agent lacks the context to evaluate non-price deal parameters.
Core components of a sell-side mandate
Inventory classification. The mandate should classify the publisher's available inventory into tiers, with different parameters for each tier. Premium placements (above-the-fold, high-viewability positions) will have different CPM floors and different negotiation parameters from standard placements. The sell-side agent needs this classification to offer inventory at appropriate rates and to avoid offering premium placements at standard-tier floors.
CPM floors by inventory tier. For each inventory tier, the mandate should specify the minimum CPM the agent is authorised to accept. The floor is not a price; it is the threshold below which the agent must either decline or escalate. The floor should reflect the publisher's yield expectations, not simply the technical minimum the platform allows.
Deal type parameters. Different deal structures (spot deals, share-of-voice arrangements, reach guarantees) require different mandate parameters. The sell-side mandate should specify which deal types the agent is authorised to complete without escalation, and which require human approval.
Audience data permissions. If the publisher offers first-party audience data as part of deal packages, the mandate should specify which data the agent is permitted to include in proposals, under what conditions, and what consent basis applies. This has legal implications: sell-side agents should not offer audience data without a mandate that explicitly authorises it and identifies the legal basis.
Approval thresholds. As with a buy-side mandate, the sell-side mandate should define the conditions under which the agent must pause and seek human review. Typical sell-side approval thresholds include: a deal value above a stated amount; a CPM below the standard floor but above a lower reserve floor (where the human yield manager may want to evaluate the deal holistically); and a proposed inventory combination the agent has not been authorised to offer.
What good looks like in a sell-side mandate
A well-written sell-side mandate allows a buyer's agent to receive clear, consistent responses during negotiation. The sell-side agent knows what it can offer, at what prices, under what conditions, and when it needs to escalate. Negotiations complete faster and produce fewer no-deal outcomes from ambiguity.
A poorly written sell-side mandate produces erratic sell-side agent behaviour: inconsistent floor application, excessive escalation to human yield managers for decisions the mandate should cover, and missed deal opportunities where the agent declined a proposal it lacked the parameters to evaluate.
Publishers planning to connect their sell-side agents to agentic marketplaces should audit their current mandate documentation before integration. The integration will reveal gaps in the mandate faster and more visibly than any internal review, and an unprepared sell-side mandate is a reputational issue with the buyers whose agents encounter it.
Who writes the sell-side mandate
The sell-side mandate is a yield management document that requires input from the publisher's ad operations and yield management teams, the legal or data protection team (for audience data permissions), and commercial leadership (for floor price and deal type authorisations). It should be reviewed on a quarterly basis, or whenever the publisher's yield strategy changes materially.
The mandate should not be delegated entirely to ad operations or to the technical team integrating the agent. Yield decisions and floor price decisions require commercial input; data permission decisions require legal input. A technically complete mandate that lacks commercial and legal review is an operational document without adequate governance.