No one can promise specific results but an ethical SEO expert can be an excellent investment for any e-commerce store or business. In a nutshell, an SEO specialist tries to get you to a top spot in search engine rankings (SERPS). Their priority isn't readability or conversions. They are focused on the myriad technical details required for a SEO-smart page.
Google depends on serving up content that people want. People want content that is either entertaining or answers a question. Optimized content pleases spider bots like Google and carbon-based creatures like humans. Create it by writing for people first (remember Matt Cutts?) and keep the focus on one big idea per page. Oh yeah, and worry about else mentioned in a Marketing Land article.