This trick let you reject a user from those with whom you share a folder with Dropbox
and decide if he can keep a copy of the shared folder or not.
- Right-click on the folder you want to share.
- Click on Dropbox / Share this folder...
- Click on the Members tab, at the top.
- Move your cursor on the document you want to undelete and click on the little arrow that points down to access the options for that document.
- Click on Kick Out.
- Unckeck the box if you don't want this user to keep a copy of the shared folder and click on Kick out user.