I have a lot of stuff piling up (Vinethorn equipment, mythical equipment, experience orbs, ferrikki galore, avatar items), but I'm not sure what the best way of selling them quickly and profitably is. Any advice on how I can offload a lot of stuff fast?

For somes items with hight demand (fabled essences, equipements, orb, old avi item ...) , you can try the trade broaker. For the other stuff there is both auction forums (item and pets), the ferrikkis should find a new home relatively fast of set for a corect price (use the adv. shearch to figure out how mutch you can get for them in average) ^-^