One of the most common mistakes when doing keyword research is forgetting to run the numbers for both the singular and plurals versions of your terms.

I have found that often times one is significantly higher than the other, and quite often the plural version is indicative of commercial intent.

Take for example SEO versus SEO Services, the former is an informational query where the intent is most likely research or information gathering. The latter, SEO Services, is a transactional or commercial investigation phrase indicative of being further in the purchasing funnel.

Another example is one directly from my business, the keyword 'traffic cone' is almost purely informational, and Google treats it as such - listing WIkipedia as the first result.

Where as 'traffic cones' caries purchasing intent, so Google instead gives priority to eCommerce websites, offering user's the immediate option to make a purchase.