I dont understand the group system and the help article is obsolete

[Comyu]

So lets say i have a folder and i scan it and then analayze all the files.
Now i want to delete all but the song of the duplicate group with the best quality.
I use the automark option and dont change any settings.
Now i click on delete marked.
But only like 1 entry in a group is marked, some groups contain no marked song even though it shows lots of duplicates
"Now i want to delete all songs except the song of the duplicate group with the best quality." How would i achieve this?

[Admin]

You can use JavaScript to mark files or auto-mark dialog (but disable all algorithms except Precise).