...an article that reads well?!

I suppose even today's rules of grammar, of which many are objective, are still subjective in the context of language. The only reason there are "rules" for the written word is so the system can be learned and perpetuated. It's a code; proper grammar--knowing it and exercising it--delivers and decodes the code. But this code is consistently tweaked and tinkered with by all of us collectively. But as long as we're operating within this system, a person still has to honor enough of this code that their writing is legible to whomsoever attempts to decipher it. Without propar spelling and grammer somethings can blur together and well become a real mess and its difficult to tell what people are trying too say so holding up you're end of the code is important. Punctuation and spelling is a bit different from UK grammar to American grammar, but the gist is the same. You can throw a document into Word, select the USA or UK grammar settings, and have everything auto-corrected. It sounds to me like your bigger problem is this person just doesn't write well. Something that's difficult to read could be totally subjective. I know a bunch of people with no idea how to read a scientific paper. They refer to it as an "abstract concept," because they don't grasp what the "abstract" is in such a paper. They have difficulty understanding the words and phrasing. It's technical. So they walk away believing it's false simply because they can't grasp it. They'll find a dumbed-down, abridged version of it online, more like a bad review written by someone else who couldn't understand it, and that's where they'll take their opinion from. Then again, some people just like different styles. A good writer can adapt to suit the needs of a reader. It's part of what makes a good writer. A great fictional story, for example, is its most gripping when the characters within are different and compelling. Of course, these characters are all created by the same person. But they often speak differently and think differently. If it's just a question of style points, this should be something easy enough to correct.

A well written article is one that sounds natural, as if it were written by a fluent speaker of that language, even if he/she is not. If a lot of editing is required then an article is bound not to read well. If one is not capable to write such an article, then he is not made to be a writer at all. Writing is after all a gift that not everybody possesses.

Well written article - Flow of thoughts and expressing one idea in a single paragraph. Additionally, the grammar must be correct. Avoid using "but" or "and" in the begining of a sentence. This is what most editors mean by well written article. The audience must be taken into consideration while writing the content. Do ask the person if he needs the conetnt to be written in American or British English and ask for an instance in your written content where words do not read well.

I'll offer an opinion and perhaps someone else can give a more professional example or at the least what they find people that pay for articles will or will not accept. My own personal outlook is about content. If an article speaks to me or gives me information that I need then I am less concerned about format. However, I want to be able to read it once and understand it and not re-read it four times to understand it. Although I appreciate and admire work that is perfect small mistakes or alternate styles or writer from other places do not bother me as much as one would think that is as long as the writing makes sense to me. On a less serious note American English lacks grammar correctness if we consider that the Brit's started the trend although we cannot understand them.