We had a lady come to our store a few weeks ago to get a system repaired. Apparently she had been to another guy and apparently he fixed it just enough for her to access e-bay. This lady was not the nicest when she came into the store, and she wasn't too happy with our recommendation to erase the hard drive and start from scratch. We did convince her that that was the best option. We completed the job, and the next morning we received a call from her. She thanked us profusely, and even sent her daughter down with a computer. A few weeks later she called us again, yelling (literally) that we didn't do a good job. We walked her through a few modem setttings, and she was up and running in no time.
There may not seem to be a point to this story, but here it is: everytime we talked to this lady, she mentioned in a not-so-subtle way about the last "guy she had work on her computer". One bad circumstance had destroyed her perception of all computer techs.
All techs out there have to be careful. Attention to detail counts on several levels. Politeness and courtesy are keys to lasting customer relations. My company advertises just to say we did. When we ask a customer where they heard about us, it's always word of mouth.