REQUEST; limit on friend request

In my site I've setup members to pay per message. However, some try to bypass this by sending loads of friendships request.
So my request is quite simple;
- a limit for x friend requests / time period

You have a custom setup, what you expect others to do?

It's not just me, I can rember people before asking it.
Also for greetings you can setup the number of alowed actions. So why not adding it for friend requests?