So 10 clients all doing this = $2000/month.
On average I get 1 call every 2-3 months. So that is significant income just to be available. As part of that (especially if it's a 10-15 minute "ssh in, do X and done" job) everybody is happy.
Note: Most of my clients are small'ish Tool & Die shops, these are the kinds of places that still run a multi-million dollar GM contract on a DOS-based MS-BASIC kludge. So my environment and the mentalities of the area are vastly different then a big metropolis like New York, LA, Toronto, etc.
They think they are getting something for free. Because I've upgraded most of their systems from the kludge to some things more robust, I do less work and get paid more.
I like working with manufacturing people: machine shops, motor rewinders, etc. One of my current clients retrofits old machine tools (think 20hp planers using 0-10V controls) with new digital controls. I always enjoy discussing that kind of stuff.