The problematic assumption here is that a given woman was paid to be there. This was a reasonable assumption on the part of the other attendees, only because there are so few women in the games industry.
So rather than the problem-to-tackle being a cat-and-mouse with vendors trying to get the most-effective promotions' staff to the venue, the problem-to-tackle is women in gaming.
If women could hit even a respectably-sized minority of the attendee audience, the assumption would no longer be safe.