Actually, I will stick up for the use of anonymous sources, even by a partisan rag like WaPo.
That's the only way the truth can get out, sometimes. When the official sources are all corp speak BS, then unnamed "people inside the company" are what's left.
Inescapably, you have to trust that the paper is not just making it up. The more they use the news to push their politics, the less people will trust them, unfortunately.