Internet let's headhunters run for a job

Marc van der Chijs of the Spill Group Asia is using his network to find a new Shanghai-based CFO in stead of using a headhunter. He post the qualifications on his weblog:

The ideal candidate would be a native Chinese with at least 5 years experience as an auditor for one of the big international accounting firms in China, plus preferably several years experience for a company in a financial management position. M&A experience would be a plus. The CFO should be an expert in Chinese accounting and taxation law (CPA title preferred), and needs to be fluent in English and Mandarin Chinese.

If I would be for a headhunter in Shanghai, this would worry me very much, since this is going to cost them clients. The situation is already very competitive and now also viral headhunting chips in. Of course, for obvious reasons this will happen first in the IT-industry, but could easily move to other sectors too, where a large percentage of the staff would be online.
Marc offers a RMB 10,000 finders fee, also for blogs that repost his announcement. But how will he know that the ideal candidate came though this weblog?