SEO Clerks seems to have reached critical mass so to speak where you can expect to find some results. As with any business just starting out most of the other sites in this sector don't have enough users to effectively accomplish what they are designed for, besides the media darling Fiverr.
Maybe. The thing SEOClerks has going for it is the price point difference. I like that they're more up front about their pricing whereas gigs on Fiverr often snark you into an upgrade in order to get the fully advertised service.
I used Fiverr a few times but I wasn't very happy with the quality, and I asked for a refund. I'd rather hire someone on a site like Freelancer.com where you can easily assess the skills of a freelancer you want to hire. As a freelancer, I also prefer Freelancer.com and similar sites. It's much easier to show your experience and portfolio there.
Freelancer.com sounds like oDesk.com. oDesk guarantees payment if you take an hourly job and use their cool time tracking feature while you work. They also offer one time payment jobs and such but those aren't guaranteed payment jobs. What I don't like as much about oDesk is that it's built more for people looking to hire than people willing to work. You have to bid on jobs and of course most jobs will take the lowest bid which is often some guy in China willing to work for $1 an hour. That doesn't work for me.
This is actually my biggest complaint about sites like that. I get that people want cheap content....I really do.... but then they often complain about it after because they got really low quality and then they're not willing to try out any better writers either. I hate having to bid on jobs against them, cutting myself down in price in order to compete, and then having to produce quality content in order to try to get more sales. Meh.
Work examples are great, set up a page on blogger or wordpress.com that links to a few of your works and link to it from your sales offers. The biggest problem with setting this up is that most forums block your ability to link to your profile or to your list of posts because they don't want people trying to get links from these places and so they block them if you aren't a member. You can set up links pointing to the forum in general but you then have to hope the buyer will actually search for your stuff, which they don't tend to do.
I use fiverr and seoclerks as well. They are the most popular these days, I remember it was just fiverr but after seoclerks was advertised in some webmaster forums, its really a hit. I suddenly got some clients who bought my video creation serbvices. And then I also tried my other services and earned few.
I think these mini job sites are the future of hiring freelancers.