Stuart, what is the website of your store and in what country do you sell? Knowing these two things is required in order to look at what's going on so suggestions can be given. Yes, it can be "manipulated".
When the google bot analyzes your website, the first page of the analytics bot is then the new home page to the collections, while the homepage has the keyword bot that will be used first.
If you want google to display the collection page you choose to push this page by way of SEO, running Adword ... after google index will choose the collection page instead of the homepage in SERP