Glitch Status: Unpatched
North of Riften is a location known as the Black-Briar Meadery. Travel there, and look for the shopkeeper known as Ungrien. Approach him to talk, and select the option "Tell me about Mavan Black-Briar." From here, you have a set of dialogue options based on your personality skill; one of the options, "Come on, get the truth off you chest. (Persuade)" is what you should select. From here, the conversation begins a never-ending perpetual circle where you can select "Tell me about Mavan Black-Briar." again and go back to the persuade dialogue option. Continuously press the speech button through the conversation to level up as much as you want!