I agree with r0ckh0und. I don't sell on eBay, but I do sell bikes off my front lawn and through CL, and I get the question infrequently. My answer is always "I like to fix up old bikes". That usually prompts the buyer to ask "Where do you get the bikes?" and that's my cue to launch into my spiel about rescuing bikes from the scrappers like lost kittens from the medical research labs, transforming the once-ugly ducking bike like magic into a shiny "new" beautiful vintage time machine, saving the environment one bike at a time. People never fail to catch my enthusiasm.

One thing I make clear is that this is my hobby, and not a business. People seem to like that it's a hobby of "fixing bikes".

I usually add that it's my hobby "gone out of control", hence the surplus of bikes cluttering the garage that my wife would REALLY like to see gone. Soon. As in right now.