All you need to do is write an application and send it to an admin.
In that application you will need to include any information you consider important.
Common sense, activity and demand are probably the most important factors.
They haven't opened recruitment threads for the clan and market section so chances are that they are not looking for moderators for that boards at the moment.
Feel free to apply anyway.
And yes, it is free work. You won't get paid. You do not need to be hampa's friend but knowing someone in the staff would be a bonus since people tend to consider someone they know more trustworthy than someone they don't.