The Persuader is an item in Ratchet & Clank which provides a varying discount to weapon (not ammo) prices at Gadgetron vendors. It was originally designed by Fred, a gadget engineer that Ratchet and Clank met at the Blarg Tactical Research Station, although they only learned of it when they met him on Pokitaru. There they encountered him in the sewers and could obtain the Persuader in exchange for raritanium (found on Hoven in the mission "Explore the Icy Wastes").
Although Fred's intention was for his Persuader to control minds, it was unable to do so and instead only slightly warps the minds of vulnerable people. The only one affected is the Gadgetron vendor operator Moby, making him lower his prices, despite him not being physically present. This is also why Gadgetron does not support the item themselves. Aside from Gadgetron, it is considered a black market device using illegal technology and is outlawed on many planets.
The Persuader discount comes down to 33% for the majority of the weapons, with instead 50% off for the weakest, and only 25% off for the strongest.