Ash here from the Shopify team. Thank you for posting your question in the Shopify Community Forums.
The number of sessions and the number of visitors on your site are based on cookies. Cookies are small files that are stored on a shopper's device, such as a desktop or smartphone when they visit your online store. When you're logged into the Shopify admin on a device, sessions from that device aren't counted as online store sessions. So in order to prevent your own website visits from being tracked, you simply need to log into your admin on the same device before visiting your website. We have some more information on the way Acquisition Reports behave over here in our Help Center.
I hope this helps clear things up with getting an accurate visitor count. Let me know by replying here if you need any further assistance on this topic.