Ghouls don't run in low health, can't be pushed and they move objects.
This kind of Undead is found usually in groups and can be dangerous for unexperienced players. Only fight them while wearing good equipment or keeping them at distance, otherwise their melee combined with life drain can do a lot of damage. When summoned, ghouls make good hunting partners because they can heal themselves, a trait that makes them good for training on as well. They are fairly slow so mages and paladins should be able to run and attack. They are commonly used as a summon for knights in training, but not so much for paladins due to the higher chance of killing them. A level 91 knight and a level 36 paladin can convince these to train. Unlike most of their undead counterparts, Ghouls leave bloodstains when damaged.
Knights, should have good skills to fight these creatures. Keep your potions handy and don't fight more than 3 at once unless you have 50/50+ skills. Also keep in mind that you cannot block their life drain without a garlic necklace.
Paladins can defeat ghouls at a low level, with low skills and ample running space, even the lowest level paladins can hunt them.
Mages: Ghouls are good creatures for experience, their loot is very good when comparing with the time and mana used to kill them. Wands and Rods are a great way to kill Ghouls easily, just remember their immunities and resistences. For a Premium Account player the easiest way would be simply to use Flame Strike.