Need Advice Regarding Marketing Agency Offer

I received an e-mail today from a social media marketing agency telling me about a competition that's going to be held for one of their clients, in the hopes I will post a story about it on my website.

This is my first offer, so i'm not entirely sure how I should proceed. As in should I charge a fee? And if yes, the fee would differ for each site depending on popularity. How do I establish how much I should charge?

Any advice would be greatly appreciated.

What are you talking about?

So a social media marketing company has contacted YOU to tell you about a competition they're having for one of THEIR clients... and they want YOU to post a story about it on your website... and now you're wondering how much you're going to charge for each of these (plural) stories that you're going to write???

Did this unknown company offer to pay you for these stories for these unknown clients? Do you know who these clients are? I guess I'd want to know these things before I could figure out what I would charge, assuming that I could charge anything.

You obviously know what i'm talking about.

The agency is called fanscape, and the company who is holding the competition is Kia Motors America. Fanscape gave me some brief info about the competition, and advised they would send me the program description with more information if I wanted it.

By having me create a post about the competition, it's a clever way of getting some free publicity. So i'm wondering what my chances are if I say yes i'll do it, but only for a fee.