Rare books. Hence, "Bibliobob." Mainly 20th century fiction and art books. I don't sell much, but I did flip a copy of "The Shining" recently for $350 (bought it for $1).

That money went towards my Geoffrey Butler build and picking up some much needed bike tools. The best part of book flipping money is that I can spend it "guilt free" on the bike habit.

Much like bikes, the internet has flattened the field of book collecting. Whereas it used to take many years of learning to spot the valuable finds, the internet has made that knowledge much more easily available (though the identification of rare books is still not easily mastered). Basically, the mildly rare books dropped in value and the really rare stuff skyrocketed.