I feel like a dick charging anybody for help, especially if I am knowledgeable in the subject. I feel like it's my duty as a good person to share my knowledge with the world. I'm mentally ill, I guess.
I do accept beer and food as payment, though. I figure as long as it's not money I don't worry about it -- they've spent their money, who cares what they do with it after that? 
I'm generally happy to help out people if they have a quick question, but if they're hopelessly lost and need hours of help to succeed, I'm not going to do it for free -- especially when I know I can make as much as I do. I don't feel the slightest bit guilty; most of these students are people who have oil barons for parents.
My typical student doesn't know anything about programming, and all of the details escape them during lecture. It's not pleasant for me, but at least I'm getting paid pretty well.
I'm getting paid by the school to be a tutor, not by the.. tutees? Tooties? Tootlets? I don't know. They also have me on a freelance list so that if people email me I can charge them, but I won't. I'll refer them to my schedule and ask them to meet me on the school's pay.
Yep, that seems like the honorable way to do it. You're getting paid, but you're not taking the students' money.
The advantages of private tutoring are significant and obvious, though: you can choose who, what, when, and where you want to tutor, and you can charge an absurd amount.
I think the demand for costly private tutoring is less amongst typical college students, but at a university with a pretty large international population, it's high. Like I said, most of the hits I got were international students, and all of them except one were students with sponsors or trust funds.
