If your marketplace is private, only logged-in users (users who have a confirmed account and who signed-in) can see the content (listings, …).
Users who are not logged-in will see the homepage and will be prompted to Sign Up to visit the website where you can customise some content to explain the situation.
What Are The Impacts Of Making The Marketplace Private
If you set your marketplace as private:
-Unlogged users won’t be able to view the marketplace listings
-Sharing buttons on each listing pages (Facebook and Twitter buttons) will be disabled
-Sitemap will be disabled