We did a trade show in Minneapolis' convention center a few years back and had the same issue. We were charged ~$1200 for a few days of Wifi access from SmartCity. Even though we paid for them to allow us to use our Wifi AP (Cisco enterprise AP, not some consumer gear bought at BestBuy) we still had to beg and plead with their on-site network engineers to get them to stop issuing de-auths on all our traffic. Then again, you have to pay hundreds of dollars to have a trash can in your booth as well. These venue are such a racket it's ridiculous.