I believe that second hand shoes, like used clothing can be a good deal. However, it takes knowledge, experience and some luck. My shoe collection is filled with second hand shoes, edward green, vass and Gaziano and Girling with a few others thrown in. Be patient, be particular and be willing to take some chances. Don't expect something for nothing very often. Better to pay more for a better shoe in better condition of you can. My suggestion is to start slow with quality older shoes made in America before 1980. These can oftentimes be had for cheap. This way your collection and knowledge will grow and mistakes will not be too costly.
As I no longer buy them I will give you (and everyone else) one hidden gem that I found to be diamonds for pennies.
Grenson Masterpiece for Paul Stuart's Choice.