It’s definitely a good idea, and won’t require resources, as the majority of sellers trying to use it for its intended purpose will have no problem clicking a report button.
Tag it up with financial penalties and aside from some fruitless whining on the forum, it’ll stop rapidly. $5 might not be much money, but to some the people who typically do this kind of thing, it represents a significant chunk of income. If they won’t listen, hit them where it hurts! It’s probably illegal, isn’t it? Oh well.
EDIT: as there’s no account penalties, the whole “I’ll just start a new account and try again” strategy will also fail. It’s fair. All that needs to be done is make sure this is made crystal clear. I mentioned the charity somewhat jokingly last night, but it’s the only right thing to do with this slush fund. Of course, if this idea ever gets put into action, I have every faith that Fiverr will make a horrific mess of it.