Besides the using of mouse you can use following keys to manage the duplicate files:
All these keys works when the list of files is in focus (click on the list if it's not in focus)
To select multiple files click on the first filename, hold "Shift" key and then click on the last filename.
Use contextual menu (through the right click on an item in the results pane) to:
If you not sure which files is safe to delete, then use "Rename files with the Prefix/Postfix".
You can easily find files that were renamed with prefix and give them back theirs names, if some application will not work properly.