You really have to make a destinction there: there are those ASKING for help, of course they should be charged.
Then there are those who just find themselves in a dangerous situation and fortunately Angel comes around the corner or jumps from the roof to save them. I think it's kind of unfair to charge them for something they didn't even ask for. On the other hand, they probably would if they had known what was about to happen. So they should pay if they want and what they can. (I think that was how it was done in the show, wasn't it?)
So, on the whole, yes, I think it is perfectly okay for them to charge.