Big problem with the Guardian is not making clear enough visual differentiation between their blogs — where anyone can write any old shit — and their actual reporting and editorial
Opinion pieces have a bright orange banner and use that same colour elsewhere in the articles, it's also used on the links to the opinion pieces. What else could they be doing to point out the difference? How could they make it more clear than heavy use of colour coding?
It was such a stupid decision for them to combine their opinion and editorial section with Comment Is Free. The latter being pretty trashy most of the time.
I think the only real way nowadays is whether /commentisfree/ appears in the URL and it isn't clearly marked as an Editorial.
I have a hypothesis that if the breadcrumb says "home › opinion" with no third level then you're in CIF, but I have no real evidence that that is actually reliable.