when flipping bikes, look for solid bikes that have ugly/aesthetically unpleasing aspects that keep potential buyers away. A buyer wants a bike typically where no work has to be done before hand to riding.

ie. colored saddles/tires/wheels/bar tape/cable housing etc. these are all easy changes that can turn a bike around and open up the buyers pool.

also when re listing bikes have the bike in a sun light outside where others objects will not take away from whats being sold. not in a cluttered dark garage.