How do I know which files to delete on Duplicate finder ?
I avoid that tool, afraid I may break something.
Your computer will not run any faster from deleting a few dupes, so it doesn't hurt to leave them be.
do a search on this forum for duplicate file finder and you should see some advice as its been brought up a few times.
here are some to get you started;
http://forum.piriform.com/index.php?showtopic=42652&hl=%2Bduplicate+%2Bfile+%2Bfinder
http://forum.piriform.com/index.php?showtopic=38640&hl=%2Bduplicate+%2Bfile+%2Bfinder
im also kroozer´s and mta's opinion. be careful with what you delete.