Without SEO You cannot rank our website in Google
All sites are ranked irrespective of SEO or other types of compliance, the search engine tries to return the results you are looking for, there are many sites, including my friends site that gets on average 3 million visitors a year and has done so for the last 8 years but he has never (or rather I have never) done any SEO jiggery-pokery and hoop jumping exercises to get that number of visitors.
Your position in search results is also irrelevant if your client knows you already from your product or via Word of Mouth which is often more powerful than any SEO tricks and oodles of cash you can throw at persuading a client to buy or use your services.
The real world, WOM is much more powerful than a search engine, WOM cuts through billions of choices as it is a recommendation by someone who has either experienced, is experienced in or has currently purchased the very product they are recommending.
So my point is this, yes, SEO can be effective and useful in getting you out to clients that may not know you are there BUT this comes ata cost because if everyone goes the SEO route, then Google and other search engines who are seeking ways to improve (by limiting results) will only have to find a new method of filtering in the future because everyone will be back at the beginning when search terms trawled up sites that had nothing to do with what you were seeking.