The Badge Seller offers Badge Pins to give you more badges to equip on the hats you wear. However, it will only offer two, spaced across the other chapters/acts. Make sure you talk to it whenever you can and have 300 Pons saved up. The first pin will require 50-100* Pons, while the second will require 200 Pons.
* I didn't pay attention the price value the first time I played through the game, but I've read some accounts of it costing 100 and some of it costing 50. To be safe, prepare for 100 and if it is simply 50, you'll have some left over to start saving up for the next one.
** The location of the two pins aren't concrete. I do believe I found the first pin in the Boss Act of Chapter One, the hideout of the Mafia. The second I think was purchased in Subcon Forest, Chapter Three, but I'm not quite certain.
With both pins, you simply have to put Badges in the slots to get this trophy.
*** If you're looking for a quick way to obtain Pons, do the Memory Time Rifts (found by completing Artifact Displays on the spaceship) as cracking open the time rift at the end will give you a decent amount every time and is repeatable.