It's fine and quite legitimate to have a prior, as your example of a perpetual motion machine illustrates. Along with the prior it's also important to understand how typical cognitive biases can affect those priors. For example, you cite the "mere experience of other such announcements being repeatedly proven wrong" and "the probability of the team just being lax with their annoucement to get publicity and grants." These might be examples of availability bias. Clearly these things happen. The question is whether they actually happen with a frequency that would justify the statement:

> Finally, I know that "we found RNA building blocks and B3" on a meteorite is less likely that contamination, so the story seems fishy and premature.

Regardless of each of our own priors and biases, respectfully, you don't know this. You don't have evidence that shifts the probability in this direction. Or rather, you haven't presented any. You haven't pointed out a specific flaw in the experimental design, instrument design and operation, data collection and analysis. What you have done is state your strong prior suspicion that something is wrong. That's not knowledge, and it's nothing that anyone else could base their assessment upon. The statement is simply a statement of your prior, nothing else. It's not a material statement about the actual paper, its data, analysis, or its conclusion.