I think that at the end of the day we are in a result driven market. If you have some experience and above all if you can demonstrate that you have achieved first page rank for even one or two websites whether yours or your clients then you should be able to confidently market your services as an
SEO consultant. Of course I am not advising you to be dishonest with your clients. Clients should be able to appreciate whatever experience you have as long as you can show some results that can be measured. Searching for the websites you have optimised on Google and displaying a first page rank is a good start. Back it up with reports generated by statistics software like Google analytics and you should be able to market your services.