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How agents compare shipping costs
An agent comparing stores works on delivered total and delivery expectation rather than item price, because that is what the shopper asked about. A store whose shipping cost appears only at checkout cannot supply either, and it is dropped from budget or date constrained comparisons rather than placed lower in them.
The comparison is on delivered total and delivery expectation, not on item price, because that is what the shopper actually asked about. A store that publishes only an item price has answered a question nobody posed.
Two filters, both commonly unanswerable
A request like "under a budget, delivered this week" contains two hard filters. Both are usually resolvable only at checkout in a typical store, which means neither can be answered at comparison time.
Failing a hard filter is not scoring lower. It is being removed from the set. See price transparency and AI agents.
Publish rules, not outcomes
A single shipping number is only correct for one basket. A rule, a standard rate for your main market plus a free threshold, can be applied to whatever basket is being assembled, which is what an agent actually needs.
The threshold has to be a value rather than a graphic. "Free over fifty" in a promotional image is not a rule anything can apply. See how to publish shipping costs machine readably.
Delivery expectation is half of it
Cost gets the attention and date is frequently the stricter filter, because a budget is often a range and a date usually is not. A stated ordinary delivery expectation is worth publishing even where cost is complicated.
The edge cases are not the problem
The objection is always the tail: remote regions, oversized items, multi parcel orders. Those are real and they are not what is blocking you. The ordinary case is usually one rule and one threshold, and publishing it moves you from unanswerable to comparable.
Name what varies briefly, so the exceptions read as scope rather than as contradiction.
Questions
What if shipping depends on the basket?
State the rule rather than the outcome. A threshold and a standard rate is a rule an agent can apply to the basket it is assembling, which is more useful than a single number that only holds for one order shape.
Does delivery speed matter as much as cost?
Often more, because "delivered this week" is a hard filter while price is frequently a range. A stated delivery expectation is worth as much as a stated cost.
What about free shipping promotions?
They help if they are expressed as a rule in text or data. A promotional banner graphic announcing free shipping is not something a total can be computed from.