I would argue that social media posts by a model-athlete can drive up ROI if the model-athlete presents the product in a way consumers/viewers can relate to. It's micro-blogging at its best if done well. I found a lot of success from it - but I am also a blogger with a marketing background so I have a strong understanding of how the "game" works. If you ever question whether someone is an honest user, view their comments. If really comes down to whether or not the model-athlete engages with their audience. Meaning, if the viewers are asking questions about the product then those are the people worth sponsoring. My two cents.