The sponsored posts should be written by the publishers. The details requested by the advertisers have to be accomplished. The post will keep the same style as the rest of the posts of the website. This way, your visitor’s loyalty will remain. This will also help the advertisers getting a higher scope. The more natural the post is written, the better for everyone.
However, if the advertiser prefers sending the text already written, it is possible to do it in the same order form.