The problem with that approach is that search engines won't necessarily show that in their extract. A lot of times, a person searches for "X", and they get a page full of results, and they skim the extracts to decide which to read.
So, say someone is looking for information on the success rate of match.com. They see the OKCupid result, with an extract that says, say, you are 12 times more likely to get married if you don't use match.com, or something like that.
If they do NOT click the link to the blog post, but instead chose another result to read, they don't see the disclaimer at the top, but they do end up having that extract reinforce the view they might be getting from other results critical of match.com.
Overall, it is better to either delete the article, or to move it to a different URL that you've excluded from search engines, and replace the original page with an explanation and a link to that different URL for those who want to see the original article.
So, say someone is looking for information on the success rate of match.com. They see the OKCupid result, with an extract that says, say, you are 12 times more likely to get married if you don't use match.com, or something like that.
If they do NOT click the link to the blog post, but instead chose another result to read, they don't see the disclaimer at the top, but they do end up having that extract reinforce the view they might be getting from other results critical of match.com.
Overall, it is better to either delete the article, or to move it to a different URL that you've excluded from search engines, and replace the original page with an explanation and a link to that different URL for those who want to see the original article.