Earlier quoted context omitted.
Wikipedia policy discourages entities from editing their own page.
I wonder if you could use a forum post of someone saying what's wrong on their page as a source to edit the page though. Forum posts aren't outside the realm of valid sources, so where exactly is the line drawn?
You could. The person themselves couldn't. (There are guidelines about the risk of bias from primary sources, which apply very much to someone talking about themselves or their own company, so you shouldn't just blindly copy what they say into Wikipedia, but you absolutely can use them as a source)