I work as an at-home VNC-based computer repairdude for the most notable repair company around. It's good work. However, because of my job, people I know in real life, and people they refer to me, they think that they can enjoy my services for free. Just as how a ______ isn't a ______ when she works for free, I ain't a ____ either.
When you take ownership of someone's computer problem, you are liable to fix that computer problem up and until any specified warranty period, whether that period is verbal or written. (I am not a lawyer, but neither is the guy I'm not helping for free.) If you didn't specify a warranty period, you've just owned that person's problem for life! Any time they come back with a computer problem, they will blame you and they will blame you hard. When I am paid to correct a problem, I let them know something along the lines of "I will fix this virus issue and any you may have in the next two days, in case it comes back".
If that computer breaks in any way without specifying a warranty, you are liable to fix it in your customer's eyes. Not only that, but you most likely caused it (whether that's true or not is up to debate)! What do you have to show for it? Turn out your pockets, that's right. Not a dime. Now you've got someone frustrated at you about an infinite problem and you have nothing to show for it.
So what if you fixed their problem and laid out a warranty? Congrats, they're impressed with your work, and they'll refer friends to you because you have a super low price. And by low I mean zero. Great, more work to do for free. More liability, more frustration.
You guys are worth more than that. Charge what you think is fair. Then double it. Your skills are not often had in this society; it's why they're coming to you. I think $40 for a virus removal is fair, so I charge $80. People pay, they gladly dig deep if I sell the service right. Expectations are set, warranties are laid out, service is delivered, everyone's happy. Then they refer more customers to me, expecting to pay $80 for a professional cleaning. Gladly, both me and them.
I find that even admitting I know anything about computers outside of a business transaction can land me in freeloader territory. It can be hard to resist the urge to come to the rescue and save the poor lady's computer, but you are not a doctor, you are not a firefighter, and this is not an emergency. Savor the negotiation, make some cash. What's the worst thing that can happen? You don't get the job, and instead continue to enjoy your time.
tl;dr Stop fixing computers for free, is terrible downward spiral. Charge double instead.