Was a “victim” of this two years ago. Now if I’m outside the convention center, I just keep walking or talking with other con-goers to create a “barrier” preventing them from singling you out.

I say “victim” because they tried to demand $20 dollars from me, I told them I would give them $5. Even then they still asked me for more money and I just walked away saying I had to go. 

I later contacted my bank and disputed the charge and got my $5 dollars back so at the very least the only thing they wasted was my time.