The point behind the 'monthly retainer' is that if only 1 client agrees to it, I make small% profit each month by doing nothing, but in reality when I have 10-20 clients all agreeing the same thing, it passive income that goes a long way.

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.