Yelpers beat it to death a few years ago, it seems.

"We stopped in while she was visiting San Francisco because of a woman outside advertising dim sum for $2.98. We never got a menu, just a few people coming around with plates now and again, so naturally we assumed the food was the advertised price. Boy were we wrong! We only got 4 plates and some sodas, but the bill came to something like $30! When we tried to talk to someone about it we were told that there was no manager, and that each plate was a different price. Our waiter acted like he had never heard of a woman downstairs advertising $2.98 dim sum. I didn't want to argue about it, since my cousin was on vacation, so I just paid the bill after a bit. But when we were about to leave the waiter came back to our table demanding a better tip! "This is America, you leave 20%" he said.

"Wow! Seriously?!

"Needless to say he did not get his 20%."