I've done gratis oil changes and mechanic work in the past for extended family members, or others in specific need. After too many situations that would fall under the heading of "No good deed goes unpunished", and without going into long-winded detail, I gave that up. Then I only did these things for my parents, our cars, and our kids cars.
I have a few select friends who I let come over to use my lift, tools, etc. But they also bring lunch, are fun to hang around, and do their own work. I advise when appropriate, and they haul away their used oil.