A number you can check before you pay for it.
Accurate means one thing here: the draft lands within an agreed variance of what your own completed jobs actually sold for.
So the pilot is a blind test on quotes you have already priced, against a threshold agreed in writing. If the engine cannot get close, you find out in weeks, for the cost of a pilot, not after an annual contract.
And an accuracy number from one shop does not transfer to another. Anyone quoting their best customer's number as your expectation is selling.