We keep learning, even late in our careers. Yes, I sometimes think the best thing I can do for a customer is to give them a good deal, but these days I am mostly successful in resisting that urge. However, there are a few situations where I don't charge my standard tuning fee. One is where I arrive to find a piano that is a disaster, like I start tuning a 100-year-old piano and five bass strings break less than 10 minutes after starting. I tell the customer that it's best to give up and get another piano, and give them advice on how to look for one that's in their budget. (I always prepare customers for this possibility when I learn they have an old piano, even though I haven't had this kind of disaster for about a year.) This kind of appointment takes substantially less time than a regular tuning, so I charge my service call fee plus a fee for the time spent. I don't lose out because it puts me ahead of schedule, and I'm usually behind.
The other situation is with longtime customers with high-quality pianos that I tune often, sometimes several times in one month. I know that these jobs will not take as long as a regular tuning, and I charge by the hour from the time I leave home.
With both of these customers, I receive an hourly rate that is close to the average I get for other work, and the longtime customers have referred many other customers to me. So I am definitely not being a sucker for charging these fees.
So yes, you should definitely not shortchange yourself. But charging less than the standard tuning fee makes sense in a few situations.