The key to have an effective SEA is to first understand how search engine optimization program works.
For example, Google wants websites to focus on providing good user experience, and it rewards sites/business that do that. To do so, it uses different systems that rely on various algorithms that analyze your search and determine what information should be displayed to you.
Those algorithms determine what the user really looking for when he/she is typing on google. That means that for a single word, you can have different variation of its meaning regarding the context of the search.
Credits : google.com
Knowing this, it also mean that people are looking for specific things but are sometimes using different words to describe them, and this can actually be the strength of an impactful SEA.
Indeed, by using words that are not directly related to your business but that are referring to it, it will allow you to attract potential customers that will probably end up buying from your platform.
Of course, in addition to the SEA, the user experience is also playing a big role in their decision of purchasing.
Also see the article "How can I boost my visitors conversions into customers ?"