I had to clearly post that I charged a minimum fee years ago. I had a guy bring in a watch he had just bought at Wal-Mart wanting me to set it for him. "It will be quick." I tried being polite and telling him that I'm not a "watch guy" and I would have to read the instructions, just like he would. He finally snatched it out of my hand when I mentioned my minimum fee. Weirdest request ever. He insisted that it would just take a minute and I should stop working on all those stupid computers for paying customers and set his watch "real quick".
By the time he left I actually found myself hoping he was as insulted as he appeared to be. The sheer audacity of someone to walk into a business and say, "Stop working on the 3 things you are doing simultaneously which all make you money and do something for me that I could just as easily do myself, do it for free and do it right now, and on something I just bought from 'not you'." Who does that? It's kind of like all the tech support calls that start out, "I just bought a <insert name of computer you don't sell>..." Okay? So you want to by a cheap computer elsewhere, but you want me to support it for free? I sincerely don't think customer understand just how asinine and self-centered it is to come to me only for the free services.