What proof should I ask for before paying a contractor?
Ask for three things, agreed before the work starts: the deliverable in its usable final form, a record of its production you can sample (steps and results for knowledge work, photos and receipts for physical work), and a written completion point you both recognise, after which payment falls due.
This question generalises beyond AI work, and the honest answer scales with the job's size and risk. For a small, low-risk job, the deliverable itself plus a written confirmation may be proportionate; demanding a full evidence apparatus to fix a door is its own kind of failure. The three-part pattern is the spine; the weight of each part is set by what a failure would cost you.
For knowledge and AI-assisted work, the production record is the part buyers most often omit and most often wish they had: the steps behind the deliverable, the sources or materials relied on, in a form that can be sampled rather than merely asserted. A recorded handover is the strongest common form, because it also carries the third part naturally: your acceptance, recorded on the record, is the completion point both sides point at.
Agree the proof in the brief, in one sentence each for the three parts. Contractors who work to standards will recognise the pattern and price it at zero, because it is how they already run their jobs. Resistance to any production record at all, on work you cannot watch being done, is the one answer that should change your hiring decision more than any portfolio does.
Checklist: proportionate proof, by job size
Small job (low cost of failure): deliverable in final form; written confirmation of completion; payment on receipt. Medium job: the above, plus the production record (steps and results, sampleable), and a recorded acceptance as the completion point. Large or relied-on job: the above, plus source states for relied-on claims, milestone records with decisions at each stage, and the export kept in your files. One-line brief clause: "Payment follows the completion point we record together; the production record for the work is part of the delivery."
Worked example
The medium-to-large form in public shape: https://zambo.dev/handover/45434a17-4afc-486a-9646-e689bcee4297 is a completed job record with steps and a recorded client decision. A contractor delivering in this form has answered all three proof asks in one link.
Frequently asked questions
Is this overkill for a trusted long-term contractor?
The pattern protects the trust as much as the money: when something is questioned later, both sides answer from the record instead of from memory, and long relationships survive exactly that way. Most trusted contractors already keep such records for their own sake.
What proof works for physical trades work?
The same three parts in physical form: the finished work inspected, dated photos and materials receipts as the production record, and a written sign-off as the completion point. The principle is portable even where the tooling is paper.
When should the proof be agreed, before or after the work?
Before, always. Proof demanded after delivery sounds like suspicion and invites argument about moving standards; proof agreed in the brief sounds like professionalism, because it is.
By Brennan Zambo, founder of Zambo.
Last verified: 2026-10-17.
Try a handover
A handover gives your client one proof link with verifiable receipts to review, then Accept or Flag.
try it: say 'use zambo to hand this over to <client>' in your ai