I wish I had seen this 6 months ago. I used to be co-operative but "my" files got changed without asking - even into cyrillic. Also requesters started sending 5 or more requests at the same time, a sort of geni form of shouting. Then people ask for a favour without saying "please", and get upset when you ask if they know what it means. The basic problem is that when you collaborate with someone you don't really know who they are collaborating with, or who they will sign up with next week.
So I don't merge or collaborate any more, simply because it wastes my time. Please stay away from my 3-greats-grandparents and below - you can build them onto your own trees, and good luck in your research.