Exactly what @amelia88 said. You will be paying some syndicate boss most probably. Also, unless you have change in your pocket, you don't really want to get you wallet out and fumble through it in a crowd looking for some cash. I've found the best way is just to ignore them, don't make eye contact and keep walking. It's easier if you are in a group because they wont feel inclined to single someone out and plead or insult you.