You might've received a message from another user who has been labeled 'BLOCKED USER'. Users get this label when it has been determined they are a scammer.
There are three places where you can report your suspicions or the abuse:
On the listing itself;
On the profile of the user;
In the conversation.
What happens after you reported a user
Each abuse report is registered and investigated by Kamernet.nl.
During our investigation we go through any history the user has and what kind of action was taken at the time (if there is any). When it is determined that the user is indeed a scammer, we add the label 'BLOCKED USER' to the profile. This alerts other users that this person is not reliable.
Depending on the type of scam, we will take further action.