how do second hand goods dealers make money?

Answer 1

More than easy

Make jumbo chocolate covered strawberries with nuts on a popsicle stick. At the mall they are 5$ a chocolate covered strawberry, sell 30 a day each one is 2$ and you will make 60$ a day if you sell all of them. And in a week you will make 420$.
and a month 2,520$
a year 30,240$ damn you could by a house sell like 60 a day
and in a year 60,480$.

Answer 2

Buy low & sell high. Find a nitch where the 'consumer' is under supplied and fill that nitch.

Answer 3

They sell junk