It is, of course, always preferable to deal with an ethical practitioner, no matter what business in question is. But SEO, by its nature, is one of most sensitive industries, and here such issues as ethics or ethical business conduct are discussed, year after year, with a lot of heat and passion.
Why is SEO special? There are a lot of reasons why SEO has become so sensitive to ethical and moral issues.
First, when it comes to SEO, it becomes extremely hard to define success and harder still to guarantee it. Your SEO consultant may be skilful and smart and do everything right way but still fail to achieve results you were expecting, because search engines' behaviour is often unpredictable or because your expectations were originally based on wrong ideas about a successful SEO campaign. Is it ethical to promise and not deliver?
Second, various spammy SEO techniques developed by crafty optimisers to manipulate results artificially add another - and very SEO-specific - variable to this equation. Most discussions on subject of ethical or unethical SEO turn out to be discussions on spam-free or spammy SEO methods.
Is it ethical to deceive search engines and their users for sake of providing (perhaps) better results for your customer? No! But, on other hand, is it ethical to place third parties' interests higher than your customer's? Is opposition applicable in this case?
The answers No, it is not ethical to promise and not deliver. So, all goals, possibilities and consequences should be carefully estimated from start. No promises without a bulletproof guarantee.
Deception is never ethical.
When SEO is done properly, there is no opposition between customer's interests and interest of all other involved parties such as search engines, their users or web.
Explanations Bulletproof guarantee
What bulletproof guarantee can an ethical SEO practitioner offer to client? Achieving #1 rankings for a targeted search phrase is a tough task, especially if term in question is a competitive one. In most cases no such guarantees are possible. #10 or #20 rankings is easier to achieve, and certain guarantees become possible, but, again, up to a point. Search engines are tricky things, sometimes they just do not like certain sites and keep them away from first 1000, no matter what is done. In many cases it would mean a penalty applied to site by this particular search engine, but not necessarily.
Anyway, SEO's efforts are never useless. Link building, for instance, will increase incoming traffic to site due to direct clicks from directories and other linking sites. Good copywriting and optimised navigation work for conversion, so even if total number of visitors remains same, sales will improve. Of course, it will involve serious studies of target market, competition and target audience's expectations and concerns. Speaking to visitors is, perhaps, hardest part of SEO art; saturating copy with keywords without breaking readability is, honestly, much easier.
For these reasons, overall increase in traffic and ROI can always be guaranteed, especially when SEO is applied in combination with PPC campaigns and other advertising opportunities.
Deception is never ethical
Quite an obvious statement, isn't it? But not when applied to SEO. Many search engine marketers will argue point violently, saying that deceiving search engines is all right because it is easiest way to achieve good rankings for their own or their client's site, and if so, everything is quite all right. "It is our job to deliver rankings", they say.