I have personally received several offers from some forum users to write posts for me in exchange for compensation, but it never occurred to me to accept something like that.
What? Does this really happen???
There are really clueless people... and others even worse, who accept this type of agreement. It's just that in the end everyone loses: those who offer themselves for this service and those who accept.
It happened (at least it used to be the case), because apparently some people saw an opportunity in it, because as beginners/low ranks they couldn't get involved in sig campaigns, so they offered such services. I considered it absurd because if you only have one account and your goal is to be on the forum, why would you pay someone to write posts for you?
On the other hand, this kind of service made sense for those who worked with alts in several sig campaigns, because that way they would earn something and still save a lot of time. But as we can see, such things are not a very smart move.