I second the notion of definite tiers to the writing community. That being said, to do a quick judge of professionalism at any price range on a forum such as DP, I'd do an immediate search for past posts - quality writers with a solid reputation will be posting meaningful responses and such, professional or not. Then I'd look for a website or blog describing services. Any writer who's been around for a length of time has worked to establish themselves in some capacity with an online presence. A blog, professional website, or possibly even that "expert" EzineArticles account show that the writer takes himself seriously in his line of work and has invested at least a bit of effort into creating staying power in the industry. Someone who has started a simple thread, not posted anywhere else on the forum and doesn't bother to treat their writing business like a true business wouldn't fall anywhere close to being "professional" in any way, shape or form in my book.