I do this in my community as well and it has really been a very rewarding experience. I started by simply advertising in a local newsletter, and also posting flyers in local stores, post offices, etc. The response has been positive, and while it is not enough to quit my day job, it has been a nice addition to my income. I don't have any kind of certification or license, only my own experience. All of my advertisements state only that I have years of experience in repairing Mac and Windows computers, which is true. I don't think you need to have any certification. As long as you can provide the service and people are willing to trust you, it shouldn't be a problem. Just remember to be fair and keep up to date with competitors wages, such as Geek Squad. I have built my business around being able to beat ANY quote given by Geek Squad, and so far 100% of the time I have been hundreds less than them. Be competitive, friendly, and honest, and you will do well.