...They need reporting to trading standards. ...
Surely you (or someone in your position) need to do this?
You've dealt with them, have information about them following your experience and have had a poor experience.
If people like yourself who've nearly been ripped off (I'm guessing others have come away with a much bigger financial deficit) don't report them, then a cast iron case with proof that they're mugs will never catch up with them and they'll carry on without any real reprisals...
Up to you though.