Demand and conversion
The rule that decides which touchpoint gets credit for a sale — a modelling choice, never a fact.
Last-click credits the final touch and systematically overstates branded search and retargeting, which are the channels people pass through on the way to a purchase they had already decided on. First-click overstates discovery. Linear and time-decay split credit by rule rather than by evidence. Data-driven models infer it, which is better and still a model.
Every platform reports on its own contribution using its own model, so the sum of all platforms' claimed conversions routinely exceeds the number of orders the business actually took. That is not fraud; it is each one counting a touch it genuinely had.
The only reliable answer to “did this channel cause sales” is an experiment: turn it off in a matched geography, or hold out a share of the audience, and measure the difference in total orders. It is slower and less flattering than the dashboard, and it is the only method that survives a change in the platform's model.
Two platforms each claiming 400 conversions in a month with 620 orders are not lying — they are double-counting shared journeys. Reconcile against the order count in the company's own system before any budget decision, and treat platform figures as directional only.
The definitions are the easy part. Whether the figure on your dashboard was computed this way is a different question, and usually the more expensive one.