That doesn't mean that we have to ignore everything they say; it just becomes us to know what the source's own agenda is, to better arm ourselves.
Craig Murray's website suggests he is, for example, a credulous believer of Russian explanations for events. He does on occasion correct himself (such as in his post about the famed picture of two different people walking through two different channels - https://www.craigmurray.org.uk/archives/2018/09/the-impossib... ) but nonetheless he has a long-standing mindset which will temper his beliefs and of course colour everything he sees and his interpretations thereof.
Of course so do we all, but not all of us are reporting on this case to the public at large, pushing our own beliefs and agenda.