I frequently flip bikes. I pick up neglected but decent bikes from yard sales and off Craig's List then clean, service and repair as neccesary. I ride them for a while. The more I like them the longer they hang around. My favorite few take up permanent residence, the rest I sell, usually at a profit of $50 to $100 depending on the bike and what I had to put into it. I've had a few that I was sorry to see go, but I can't keep them all. It's kind of a rotating N+1 system.