How exactly do you make money these days?

Merchanting is effective, but takes time and dedication. It's as simple as keeping track of price trends and noticing outliers. The reward comes, but not quite as quickly as some people are willing to wait for.

As for a guide.. well, there's probably one floating around somewhere, but it boils down to common sense.

• Check FM often. All of it. Not just the bottom row, and not just the top either. Record common price ranges for items. Check to see that items are actually selling.
  
• Visit the FM Entrance in channel 1 and compare these prices with the knowledge that the people selling outside aren't spending NX.
  
• For items that can be crafted in one way or another, consider the cost of materials and the amount of demand, along with the selling price of the crafted item.
  

Those three points should give you a very, very basic idea of how to merchant.