Can we filter free items on marketplace?

Is there any way to show only free items ?

No, there are no filters on the marketplace.

Most free assets are from Epic Games:

Few other ones I remember:

You could find some high-quality assets in the learn-tab of the UE4-launcher as well.

For free assets check my thread: Free Community Assets - Community Content, Tools and Tutorials - Unreal Engine Forums

Marketplace its focused on paid, even if you want to publish something there is a minimum price, only epic games can (with some exception):