SEM is about cost per click (CPC) while SEO is about free traffic.
With SEM you can set a specific landing webpage. With SEO, the search engines decide the most relevant page. The difference is in control, cost and result obtained.
Since everything happens in seconds, the visitor’s decision defines the profit amount. If they don’t click on your website link, then the competitor gains the benefit. SEM gains an advantage on that field but with a cost.
Optimisation of SEO, based on searched keywords offer a great and no cost benefit.
The sales potential in both cases depends on how relevant your webpage is to the visitor search. Website design also affects sales. Sales conversion increases with plenty of A/B testing. A professional search engine marketing company is the way to go to improve your landing page.
SEO and SEM efforts are measurable with ROI, when the viewer becomes a visitor (conversion). Search engine marketing services initial cost plus advertising cost, makes it a difficult decision. So, SEO services have an initial and final cost but with a long-term benefit (and no advertising cost).
SEM provides immediate conversions, sales and future sales forecast. SEO should not be ignored or applied moderately. SEO is an essential method to get extra income.
SEO is necessary to start your internet marketing promotion efforts. SEO provides free traffic. SEM provides more control, immediate results and more sales. Website optimisation and sales improvement, allows the next step to SEM.