----The person may be unsure of your willingness to receive this information. In other words, there are many reasons a person may refrain from giving you potentially helpful information and still have a mental stance of "friendliness".----

I agree. For instance, if you know that people would over-value your evidence. For instance, what if Walrus believes that Carpenter is over-credulous. He thinks that Carpenter will take the evidence, proclaim 100% certainty that pigs can have wings, and go blow all his money trying to start a flying pig farm. Walrus believes that there will be a higher cost to Carpenter of overconfidence in the belief that pigs have wings, and a lower cost to underconfidence. Consequently, Walrus will keep his evidence to himself because he knows that Carpenter will receive it with bias.