I think what keeps a lot of folks away from professional SEO is that the techniques aren’t very consistent and the results for poor techniques are at best temporary. The advice that stands the test of time seems to be things you should be doing anyway. Build great content, figure out what you want to say and say it consistently, focus your market, empower your fans to link to you, title pages appropriately.
I’m not saying there’s no value to some good research into how people use search engines but techniques to get that elusive first page ranking quickly are historically a string of things that are later downplayed by the search engines and rendered obsolete. Ask the folks with huge meta tags or background colored keywords in their footer if that time and money would have been better spent building great content and marketing to potential customers/users in other ways.
I’m actually all for professional SEO if it’s done ethically with realistic expectations and sustainable practices. These techniques tend to be less concrete and therefor more difficult to market than “We’ll get you ranked in the top ten by next week for ‘peanut shell floor coverings’”. People want to know what result they’re getting for their money so firms tend to give them those type of promises.
Everyone should get their site looked at by someone who knows what they’re talking about in order to make their content accessible to the search engines. Beyond making it easily accessible, focused, and appropriate most of it seems to be short term fixes that will need to be revisited.