When the time of the booking has passed, both the punter and the WG can leave feedback, but neither can leave a rating (positive, neutral or negative) until the WG has changed the status of the booking to "confirmed".
Hence the following scenario:
Punter has a crap punt, but the WG knows this and won't confirm. Punter ends up posting a "feedback only" comment about how crap she was.
WG then confirms the booking. She flags the punter with a negative, alleging that he stalked her, raped her, and strangled her cat.
Punter then "disputes" the feedback, allowing him to defend himself (probably hitting the message size limit). This doesn't remove the malicious allegation, but it no longer counts against his feedback total.
The only real use for this system is that you can at least see that a WG is genuine, if she has feedback from punters who themselves have feedback from known WG's.