Upload & Sell: Off
I don't really dare to do these, I had one or perhaps two that I did a while back but they didn't turn out very well. Too many things can go wrong (especially in crowded areas like most of Vegas). People can get in the way, local security can turn away the photographer, etc...
I kept hearing voices at mine. It was in a Christmas tree farm and I thought I was going nuts. But it just ended up being a bunch of random families. I almost had to shoo one family away from the tree that was decorated with "Marry me?". I also couldn't tell if it was the bride and groom's voices I was hearing, or other families' voices.
I'd be afraid to do one in a busy place like Vegas, so I can totally understand. I'd hate for someone to pay me and then turn around and say, "Listen. You picked the spot, not me. And the security guard kicked me out, after 1,000 drunk gamblers walked in front of my camera." Scary, indeed.