I am not all familiar with SEO Clerks. I joined Fiverr 5 months ago, and I am primarily a Fiverr translator. I must say that there are a lot of SEO related gigs to be found on Fiverr such as article writing and so on. However, I have found out by having had an article writing gig myself on Fiverr that there are some Black Hat SEO people that are active on Fiverr.
Sometimes, I got the idea that it did not really matter what I was writing for those people, as long as their keywords were mentioned enough times.
That is not my idea of SEO, I guess that is why I call them Black Hat SEO people, I suppose. In my view, SEO is here to enhance the content and not to become the content. Though my article writing gig had 100% positive rating, I suspended it and continued to only be a translator. It is just something that I did not want to be a part of.
So I would say that Fiverr offers good SEO opportunities but that you have to be aware of both the sellers and the buyers that are out there.
In my view, it would be a good idea that Fiverr would deny some kinds of gigs and/ or monitor the behaviour of certain buyers. SEO is such a useful tool. It should not be abused.
I will look into SEO clerks though!