I have been fined for crossing a solid white line, and that was by CCTV. That also was near BKK and I was a bit confused as to what ramp to take, the road behind me was completely void of any traffic, otherwise I would not have done it.
The fine is 500baht and nothing more, yes the cops were trying to rip you off, I have my dash cam, positioned, so I can turn it round to my drivers window, just incase anybody tries something wrong.