WooCommerce – prevent multiple orders?

In my shop there is a special offer which should only be orderable once.

I don’t want to enforce user registration, so I have to compare the current billing address to the already existing billing addresses in the order records.

In which hook should this be done and how can I output my own error message? I would be very grateful for any hints.

http://docs.woothemes.com/wc-apidocs/hook-docs.html
It’s a pity that this reference doesn’t contain short descriptions for each hook.