I really mean “no” when I say “no”
I've noticed a very annoying pattern recently.
The past couple of times that I've gone to a trade show I've been very careful to select the option that's roughly "Do not share my contact information with any vendors."
Despite this, I've received lots of emails and phone calls from vendors who want to follow up on my recent visit with them at the shows.
Now I'm very careful to not let people scan by badge, so I can be reasonably sure that these guys didn't get my contact information from me, which leaves the shows' organizers as the most likely source of this information. Despite the fact that I explicitly told them not to share it.
Even worse is the fact that privacy is one of the hot topics at these shows now and every vendor is talking about how you can use their technology to ensure the privacy of your customers' sensitive data. Like their phone number and email address.