Looking for bloggers to write about marketing/advertising

Num. of articles: 1
Words per article: 500
Information for the blog/website: We list marketing companies
Topic: Marketing/Advertising
Tone: Formal/Professional
Outline & Structure: I operate a marketing resource website (a yellowpages of online marketing companies) and I am looking for one time or ongoing writers to come up with relevant content to add to the website blog.

Topics I am most interested in are: social media, local Marketing, SEO, SEM, any other topic related to ONLINE marketing/advertising

I will provide keywords for the topic(s) you choose to write about. Article length is flexible with a minimum of 500 words OR 300 words with a strong visual/infographic. Content must be unique and price will be negotiable based on your expertise ($25+). English first language users only, no writers from India please.

Please provide sample writing that is relevant to the topics listed. Writer must be very familiar with topic he/she is writing about.
Extra notes: