I've got various answers to this. My first real flip deal was those 4 ebay bikes the other week. They were all beautifully maintained, and ready to go straight back out the door. Bike number one, the Bates track bike, has more than covered what I paid for all 4, but the other 4 don't have the same vintage appeal, so they're getting parted out and sold that way. Little or nothing to do there.

I also have 3 mountain bikes to sort out for friends - all need no more than lubrication and cables, that I can see, and I'll only start greasing bearings if there's a real sign of need. I have a road bike that I got in a package deal with a BMX for £10, that I'm doing up for a friend. The rear wheel was borked, but I got a campy/shimano wheelset for £5 that only needs a new tube. This bike has Cinelli bars and stem, and since I bought another bike to convert to singlespeed where I'm swapping the bars out for some chopped ones, I'm going to stick the bars, stem and levers from that onto his bike (benefits him, he gets aero levers), and sell the Cinelli bars and stem, which may even put me in a small profit on the whole deal.

When I have the energy, I trawl ebay for badly described bikes, and for parts that for some reason aren't selling, but I don't do it all the time. Thrift stores and charity shops here just don't do bikes, and I've yet to find a reliable source apart from Ebay....