Are you really willing to assume someone spelled their own name wrong before you question your own knowledge about Dutch names? That seems a bit unreasonable. It's much more likely that your assumption is incorrect than someone wrote their name incorrectly.

This is the premise that should drive software as far as user input goes. The rule should simply be "Trust that the user entered their data correctly and don't try to 'fix' it programmatically." Validate it, sanitize it, but don't change it.