I think it's a great idea! Do it! If you have all the tools, equipment and most importantly skills, try posting on craigslist.org. If I new how to fix everything on a bike I would do this. Advertise as if you were the bikeshop doing business (of course mention that you are a guy working out of your house) i.e create a name, mission statement, price list. For price list go to an established bike shop, get their prices and then offer your services for at least 50-75% lower, or really cheap. Don't offer anything high-end or expensive, at least in the beginning. You will probably get a good response. See how you like it, change your business model may be, tweak you shop, get more tools. After a while you'll get known and have a good customer base. Now you ready to move up in the world and charge people more money for your services!