Question regarding combing or merging trees

[Grundei]

I have a second cousin who has a tree he has named (hypothetically) The Smith Tree. It contains many of my relatives and lots more that are not my relatives. He wants me to "share" mine with him on Ancestry.com. I know that in some cases I have better information than he has (my birthdays are from more reliable sources for example) plus I have nothing to do with the "Smith Family" other than being a second cousin to one of them.

Question - If I share my tree with him will my data still be my data? What if there is a conflict in dates, or names or whatever? Do I somehow inherit his?

Is there any downside to sharing?

Thanks

[Guest]

if you make sure you only invite him as a Guest he cannot add anything to your tree so cannot mess yours up
Go to Tree settings then Share your tree and there is an option for Editor ,Guest or Contributor .