There's some subscription-based data processing web service - users pay via PayPal for the right to use the service. The "terms of service" document prepared by lawyers explicitly says that there're no guarantees so customers can't possibly file a lawsuit.
Now the service doesn't always work trouble-free. Sometimes there're network problems and so it's unreachable to some clients. Sometimes there's a problem with third-party services the service depends upon. So something like twelve hours per year total it doesn't work. This is not perfect, but IMO very good.
Yet clients feel that since they've paid for it - it must just work, period, at all times and they even write claims for compensation to the service support.
I'd guess they just don't read the "terms of service" but I can't be sure.
What's the standard practice (besides having "terms of service") to prevent users from having unreasonable expectations?