Kamernet.nl is unfortunately not able to check whether the person who's listed the property. Many properties are listed by people who are looking for a new housemate and with the approval of the owner and landlord.
The rental agreement should always be signed with the landlord or rental agency. When you sublease it is not necessary, but it is advisable to check whether the landlord is aware of the sublease.
You can check who owns the property through the website of the Dutch land registry. This website is not in English (only the About page), but when you go to the homepage and fill out the address for your new potential home in the big search bar at the top of the page, you can compare the name of the owner and the name of the person you're talking to.