The field still seems fairly undifferentiated, so 'space agency' seems to cover space travel, astronomy, satellites, and anything else outside the atmosphere. Who else is more credible, someone from SETI?
Anyone with actual proofs, I think. We have to filter the source according to the type of information: a political tabloid isn't a good source of information for science, even if someone post it on HN. An accredited scientific journal is a good source. Furthermore, it's necessary looking for "red flags" in our source (critical reading): if the source has few verifiable facts or no verifiable fact at all, maybe it's a case of "alternative fact" (aka bullshit). The search for alien life is taken seriously by the scientific community and a researcher has all the motivations to be part of the history proving the existence of extraterrestrial intelligence. If you ask me, I am "probabilist", I think that they could be out there. I'm waiting for evidences. This article is not.