I don't think there are too many products that you can make money from buying. The few I can think of are things like bee hives (paid to remove it and paid for the bees), dirt/sand in abundance areas (I'm not sure they sell it), and other natural resources. Most of them you're getting paid for removal and not buying though.
Housing and real property can sometimes effectively work that way, where you are paid for buying because you are taking on responsibilities by purchasing the property(say, for liens, cleanup, etc)
