Data work is easy to buy and hard to buy well. The difference shows up in the first deliverable, which is why the evaluation should happen before the project rather than after.

Ask for a sample — and read it carefully

Ten rows tell you more than any portfolio. Check accuracy first, then formatting, then how they handled ambiguity. If two of ten rows have a formatting inconsistency, two hundred will have twenty.

A supplier who will not send a sample before a paid engagement is telling you something useful.

Listen to the questions they ask

A good partner asks about definitions: what counts as verified, how to handle a missing field, which country format wins, whether a partial match should be merged or kept separate. Those questions mean they have done this before.

A supplier who simply starts without asking anything will make every one of those decisions for you, and usually not the way you would have.

Look for process, not promises

  • Source tracking per row so any error can be traced
  • A defined verification method, stated precisely
  • Deliverable format agreed in writing before the work starts
  • A stated revisions policy with a clear definition of an error
  • Regular progress updates for anything longer than a few days

Warning signs

  • No sample, or a sample with obvious errors
  • Prices far below the market, which usually means automated output with no verification
  • Unwillingness to name the sources used
  • Deliverables in screenshots instead of actual data
  • Vague answers about how the data will be verified

The real calculation

Compare the cheap quote plus your own cleanup time against the careful quote that needs no rework. In practice the second option is almost always cheaper, because cleanup is slower than original work and far more frustrating.

The cheapest list is the one you do not have to fix.

Start with a small paid batch

Rather than committing to a large volume, commission two hundred rows and review them properly against your own spot checks. That single test predicts the quality of the next twenty thousand far better than any conversation about capability.