That is a good question, and one that any professional user of the professional defence press has to face. The only solution is to read, and over time find out how reliable each journalist is.
Journalist A might be good on the politics of defence procurement, but weak on technology.
Journalist B might be good on warships and naval technology, but a bit shaky on aerospace.
Journalist C might be good on technology, but have a poor understanding of tactics and operational matters.
Journalist D might simply be an ‘also ran’, struggling to cope, and likely to face a change of career before long.
Journalist E might be an experienced combat officer, but with little understanding of the practical problems of high-technology manufacturing.
In short, they are like any other profession - some are extremely good, some are bad ‘uns, but most are fairly competent at their jobs. If they were not, they would soon be swelling the ranks of the unemployed. It is like any other job – if you cannot to the job properly, you will be fired.