Taking advantage of komponisto's link, I quote from Chapter 5, pg. 505:

Indeed, the very evidence which the ESP'ers throw at us to convince us, has the opposite effect on our state of belief; issuing reports of sensational data defeats its own purpose. For if the prior probability of deception is greater than that of ESP, then the more improbable the alleged data are on the null hypothesis of no deception and no ESP, the more strongly we are led to believe, not in ESP, but in deception. For this reason, the advocates of ESP (or any other marvel) will never succeed in persuading scientists that their phenomenon is real, until they learn how to eliminate the possibility of deception in the mind of the reader. As (5-15) shows, the reader's total prior probability of deception by all mechanisms must be pushed down below that of ESP. [emphasis added]

The point I was drawing was precisely captured in Jaynes' caveat - the advocates must, if they can, provide evidence to eliminate other possibilites.

Edit: But I forget my point: they must if they can, but if they can, they will overwhelm the differing priors. Educating a person with poor priors - or poor assumptions in general - is inconvenient, not impossible.

As I do not have access to Jaynes' book, this response is rather less than useful. I assume that Jaynes' example relates to observing just the demonstration of psychic powers - what I am suggesting is that further observations, causally related to the demonstration and those features which may suggest or oppose fraud, can overwhelm this initial difference in interpretation.

I think you might want to reconsider the scope within which appealing to differing initial assumptions is valid.

This reply seems to be an illustration of the above discussed appeal to authority.