I do most of my purchases on line for both cost and convenience but would never ask a shop to do work for no charge.
A couple of years ago I was building up a new frame and fork and the crown race on the headset was a very tight fit. Since I didn't have a race setter at the time I took the fork and crown race to a nearby shop and asked them to set it for me. I was there mid-day on a winter week day and they weren't very busy so the mechanic did it right away. I offered to pay, which I was more than willing to do, but they said no charge. I have bought from them in the past when I needed something right away and will certainly do so in the future.