Years ago, on my own, when I used to attend, I used to call the venue about a month in advance and explain to them what was about to happen. Sort of a warning, per say. I explained, in detail, who NANOG was comprised of (I often would use the term "operators of the internet"). I explained even if they think they have seen this before, they haven't. Some listened. Some didn't. This would be something I would be willing to volunteer my time with - discussions with, and negotiations with, venues. It's all in the approach.
Holding the last 10% of the meeting room payment seems like a good start for any venue.
But as others have indicated, the market may be too small for free- market principles to be fully effective.
I tried this approach many years ago, for a Blogher conference. The hotel's IT people were uncooperative, and incompetent, and they lied both about their network design and their equipment capabilities. I have since learned that this is par for the course. IMHO the only way to solve this problem is with big $$$ penalties in the contract, big enough that the incompetent IT people realize their jobs are on the line and relinquish control so experts can get access and set-up things properly.
Also note - the conference or hotel's IT people will always claim they have "done this before with no problems" even when they haven't.
jc