Perhaps a solution to this could be to give the interviewee something that only he can give the interviewer back when they meet. Something that the interviewee cannot pass onto the 'real' candidate who will appear on the first day. On the other hand, fining the real candidate is the worst way possible, it has to be better than that.
It can help prevent this attempt of 'baiting and switching' to a lesser competent candidate in the first place.
The attitude should change from 'Oh I can give this test, I'll pass it for sure and you can pay me $X for it', to 'Screw that, they'll find out immediately that it wasn't me.'