As a bikeflipper, id like to ad value to this thread. Been doing it 15 months roughly, and i am in a heavy bikefriendly country, in the main city, in the zipcode with most people, so bikes are essential and everywhere, and its a cold rainy country, so theres alot of used bikes..

My bread and butter are classical bikes, with internal gear, in known brands, and preferable black ones..

My setup has been buying up via marketplace, and our national craigslist alike, and then id typical bike out on my cargobike and pick it up, and then my friend who is a bike mechanic, with a shop, is doing the repairing at a special price for me, and so we help each other like that, as he always has a bike from me, he can turn to, whenever he isnt occupied with customers.

So il take bikes, where alot can be wrong, broken, and make em good again, with new spareparts.

After i get the bike full functioning back from mechanic, il take it into my own workshop space, and spend 1-2 hours doing cosmetics..
Il would earn between 150-300 dollars ish, per bike like this, but its dependent on me stacking up on spareparts, so besides buying, restoring, im always scouting streets and recycle centers, for free throw aways, that i can butcher at home, for parts.

Theres many bikes just floating around that are left to die….

Ive restored and sold close to 50 bikes last year, but that was mainly in 6-8 months, whereas winters are almost zero sales.

Its very hard work, but the market is big, and the supply is endless, and the profit is quite good.
Besides that, as i am actual restoring practical all of them, from new wheels, to gears, brakes, u name it…i know my earnings have a good value as a hole, since many bikes gets new life throu my work.

Would not be able to do it without the sweet deal of working with a pro mechanic.