I enjoy teaching people new things in general, but what I win specifically depends on the situation. With friends and family, it's the personal satisfaction of helping someone I care about.

With customers there's the added benefit of improving business relationships and building trust. If someone contacts me with a question, and I withhold the answer until they pay me, they're gonna feel cheated when they realise the answer was pretty straightforward. It doesn't matter if, technically, I'm providing a service and I'm within my rights to ask for compensation. That customer is going to hesitate to return in the future, because they now feel I just care about their money.

Being open, transparent, and helpful has the opposite effect, in my experience. The customer feels at ease with me, they trust my judgment, know that I'm looking out for them, and so are happy to return to me when they need something, and pay for the job.