Books, an the reselling of them

My experience selling used/old books is the books that your going to make the big money on are old automotive repair manuals especially from the sixties and fifties also tractor farm equipment repair manuals like Ford farm tractors, International, Massey Ferguson, John Deere farm tractors both vintage and later model repair manuals. Also repair manuals from Asian farm tractor manufacturers like Kibuto, Mahindra etc. Other high profit repair manuals-All motorcycle, ATV, boat outboard motors, jet ski water craft repair manuals with the vintage Harley, Indian manuals including vintage motocross bike repair manuals from Bultaco, Montessa and Maico can sell for outrageous prices. And finally if you are not offended vintage porn books are highly sought after because they are very rare because it used to be outlawed. The Vatican owns the most valuable collection of porn material in the world and is considered one their most valuable investment holdings no joke. These books can be found about as easily and as cheap as any used paper backs.