A character performing a persuasion check should attempt to describe and act out their persuasion.
Once complete, the GM should evaluate the description, and use that as a modifier to the persuasion roll.
A character that says "ummm, IDK, I guess I just try to influence them using my high charisma" should get no modifiers to the roll. A character who tries but entirely flubs the conversation should get a -1 (when appropriate), a great performance with an entertaining flourish to the description should get at least a couple ++ to the roll.