How to write blog post

I'm not sure exactly how these Fiverr sellers are doing articles, but a few thoughts are as follows..

When it comes to affiliate review articles, I think that most are either simply rewriting other articles.
Maybe find 1-4 articles (or Amazon reviews) on the same product, and cut & paste them into a new article, then rewrite it with spinning software, to make sure it will pass CopyScape.

That being said, you are really not offering anything new to the reader, and Google know this, so I doubt that the article will ever rank and will be viewed as more or less "useless".

If you are only interested in spitting out some easy content to sell, then OK, you most likely don't care either way..

I recommend you to read this article by Neil Patel.

Some time ago I wrote a blog post for a website. Here are the guidelines I followed

The article must be completely written by yourself. Never copy from somewhere else, copy and edit or scrape.
Grammar should be correct
Write according to the given title or keyword
You should include the given Keyword in the first paragraph. And for that, Backlink should be applied if you have not given an Anchor text
Word Count should be 350-500 (Check Keyword density and include the main keyword and related Keywords to the required amount
You must give priority to the main keyword and as to the requirement, use related Keywords
Keyword should be included in the site heading, post title, first paragraph, in a subheading (h2), content, and in the final paragraph if required (should manage with the word count)
Insert images/videos if necessary
Blog URL must contain keywords ( for BL blogs )

btw, this "keyword" thing is no longer valuable as Google is not considering it anymore. But, using it in URL and placing it in several places in content is could be useful.try to make your content unique and useful for readers