Who decides whether a pick won

A result taken from a public source that the seller does not control. If the person making the selection also grades it, the grading is part of the product being sold.

The conflict is structural rather than a question of anybody's honesty. Ambiguous cases exist in every sport — a void, a line that moved, a market that settled differently at different books — and whoever resolves them is making a commercial decision.

Naming the source in advance removes the conflict entirely and costs nothing. It is one sentence, and it can be checked against the source afterwards.

What follows from that is less comfortable. Sellers who grade their own results rarely mention that they do, because it is presented as an operational detail rather than as a term of the offer.

What to do with it. Ask which public source decides a result and what happens in a void. Both answers should exist in writing before you pay.