What does it tell you when someone says "I don't believe in evolution"?

Yes, but this is key you both my and Humbabella’s points - science by necessity contain first hand accounts. Many of them. That makes belief in science very different from any other kind.

Beyond the existence of the group consensus of first-hand accounts, though, while they are necessary they are not continually the most important factor. Once consensus is reached, continually demanding first hand repetitions becomes an outlier activity, individual and trusting only of one’s self, when in fact application and additional new theories that can be tested is much more productive and actually challenging, though these only come about when people accept the original theory and move on. But accepting and moving on requires belief in the consensus. If we didn’t do this, science would never advance.