Merch
and
Flipping is the same thing.
I'll explain.
Merchanting is buying an Item when the price is low, and waiting(or manipulating the market) and selling when the price is high.
Flipping is buying an item when the demand is high(peak times) and selling when the demand is( when america is asleep).
Flipping can be done relatively quick(less than a 24hr span), merchanting may take a little longer, but can get you much higher profits, but may require a mass to manipulate the system.
Both involve supply/demand. Both being the same thing essentially.