Guys, you aren't going to want to hear this, but people don't value computer work. They think it's something less valuable people do, and should be willing to do for free. People also don't respect anything that's free. If you work for free, they will expect it. If you work for free, and fix it, but it's not exactly like they imagine they want it, they will STILL be angry with you.

You can do what you want; however, I learned to simply stop the freebies. I learned to be very direct about the fact that this was a business transaction, and they would have to pay me a great deal of money UP FRONT in my PP account, and sign a work agreement. (Actually it's on the PP invoice, by paying, they acknowledge the terms.)

I learned the people who had a problem with it were the people who were going to waste gobs of my time. They also would have had no sense of appreciation, so they would have done what your dentist friend did.

It's up to you, but if you keep giving it away after you've seen this dynamic in action, there's no point crying about how people treat you.