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I'm aware of TeamViewer screen sharing, however, the risk is that people might call me a scammer because it allows me to control the computer which I'm connected to, even though I have no malicious intentions. So what app should I use instead?
How high should prices be?
The software you use now is quite good, I already tried to use TeamViewer. There are a lot of other alternatives besides TeamViewer.
Try some open-source software for screen sharing like
https://tigervnc.org/ or
https://www.tightvnc.com/.
Your kind of service is possible here, try to make your thread in Services section and you just state what you can do and just name your price, start with the minimum, or based on how difficult the work is.