Undoing bad merges is one of the things that curators on Geni can do. I believe that we all have a responsibility to make sure that tree matches in our personal branches are checked regularly and either approved or rejected. Personal knowledge means that we can see if people of similar names are indeed matches or not. If we don't regularly clear these matches someone else will come along and make bad merges which those who are familiar with the branch of the tree could avoid.
Visit your matches regularly - https://www.geni.com/list/matches?filter=tree_matches
"to make sure that tree matches in our personal branches are checked regularly and either approved or rejected."
It needs to be pointed out that with growing personal branches... in my case over 50 thousand individuals, it is not realistic to do this. My only work would end-up being "checking regularly" (!)
What we'll need to combat bad merges is more relationship locking in Master Profiles.
That said... I do clear GENI tree matches frequently. But, long ago, I see this as an endless task. I wish that matches that don't have suggested dates of birth/death were not included in whatever search engine paradigm chooses them.Location matching doesn't seem to well developed either.