Off the cuff solution: Require accounts be tied to a real identity (provide driver's license #?.. No I haven't thought about legal/privacy repercussions) and introduce a post-date rating system. Sprinkle in some sort of staleness algorithm along with an anti-maliciousness algorithm (IE: someone who always rates their dates as creeps might themselves be a nutjob) and perhaps the system can survive.

Off the cuff so tear this to pieces. Perhaps I just WANT the idea to work so well that I am not seeing the forest through the trees.