Hi, this is not an ordinary service, but it might be useful...
I can comment, on your behalf or not (meaning with my FB account, or yours), on posts you are interested to keep on the top of a certain Group/ Page etc.
You can keep the relevant post with a high exposure very easily.
The budget is per comment (for example you can define that you want a new comment every 3 hours, price per comment is very low), and when I comment i delete the old comment, so it will not overload the post and look ridiculous...
Please note - I do not create the post, i need details about the post and I only comment on it.
Regards