Assuming "quality" means accuracy/truthfulness, how can the average reader rate the quality of any writing?

That's a strange question. Do you perhaps mean: as opposed by judging by proxies like nuance, complicated sentences, absence of sensationalism, etc?

Hindsight is one way. A reader looking for quality publications can wait a month, reconsider and form a conclusion.

Yes. But what conclusion can time bring? What independent conclusion can be better formed at a later date?

(This feels weird.)

Newspapers often print news. Things not yet confirmed or denied elsewhere. Today I see a headline about which ministers knew about a particular evil deed before it was too late. Right now the article rests on anonymous sources, in a week all of of the relevant people will have spoken on the record.

The fairness of a summary or clarity of an interpretation is similarly easier to judge after the people involved have had the opportunity to react to the article.