Ask HN: how to buy SEO? Can SEO be automated?

We need SEO but I don't know how to buy it effectively. Getting value for money seems to be a challenge - How do I know what I am buying? What should I pay? Do I need to be paying a monthly retainer to an SEO specialist? Is there an automated SEO service that allows me to put in my site address and it tells me what needs to be done? How effective or not would this be? How closely related to SEO is SEM? Should I be buying SEM services at the same time? How to tell the SEO charlatans from the SEO wizards? Any hints and tips on buying SEO would be much appreciated. I feel like I am buying services from a car mechanic - they could charge me any amount of money and provide any level of service and I wouldn't know the difference.