When I receive a call for service we begin with some basic information about the problem. When it becomes apparent that there may be some things the customer can check and possibly diagnose or fix it himself that is always my first choice.
Likewise, many of my customers call me for advice. They know I will guide them to the answers as best I can over the phone. For free.
This is a loss of time and the immediate job, so basically nobody does it. But I do.
My belief for many years has been that if I can help people do for themselves what they can at no charge then when they have an issue they can’t handle they will call me first.
For long term business, and in repairs this is what I rely on, I believe it not only to be the right thing to do, but the best practice for obtaining and keeping customers.