I think the only way to take power off these thieves is to refuse to use them. I know some of you take a lot of bookings through these sites (which we didn't) so it may be a case of easy to say. We had all sorts of issues with these sites and in the end we decided they just weren't worth it.
12 to 15% commission is just outrageous, especially when their contracts say that your own site's rates can't be lower.
We just upped the rates on their sites and nobody said boo, then we decided that advertising ourselves on their sites with inflated rates was counter-productive......we ditched them all and haven't been happier.
The questions I would ask: What is your profit margin? Because 12-15% takes a big bite out of it I would suggest. Is the extra traffic really good for business or are you just making your occupancy stats look better? Are you just attracting bargain hunters who wear out your rooms for no return?