You will find ads like these on oDesk where the employer has a client and wants to subcontract work.
How do I know?
The employer only wants to increase the number of likes for their facebook page. It doesn't matter to them where the actual Likes are coming from. They just want that number to go up.
Big "Like" numbers can hook casual facebook users to click on the like button as well. Social proof. If the posts and content is not something they were looking for, they start looking for the "Unlike" link. After that, it's going to be that much harder for you, the facebook page owner to get them back.
Also, keywords such as marketing "guru, expert, ninja, rockstar" and anything similar to these are dead giveaways. If an employer wants to hire such, that employer doesn't understand the underlying principles at work in Web 2.0.
If this was my own business, I am NOT going to look for community managers who will do the job for the lowest price. The lower the price, the lower the quality of work.
This person that I am hiring, his/her task is to engage my audience. If hiree doesn't do a good job, it reflects on my business. I save money paying for hired hands, but lose business at the end of the day. That's not a winning proposition for me.
I'd rather look at their portfolio. I will also consider how their cover letter is crafted. Resume's are boring. Everyone is a super hero in their resume. If they pass that hurdle, I go chat with them on skype in real time. Community managers engage people with written words. The skype chat interview is better than talking to them. This way, I will see how they structure their words to convey meaning.
I shared an article recently on this site, "How to find good talent." The article explains why good writing is important in today's social web.