He used to sell Fireball before the winter update 2007, after that update Fireball became a premium spell. Also, on a blackboard is written you can buy a Spellbook, this is however not possible. Muriel wrote the following books:
Player: hi Muriel: Greetings, Player! Looking for wisdom and power, eh? Player: job
Muriel: I am the second sorcerer. I am selling spellbooks and spells. Player: sorcerer
Muriel: A sorcerer spends his lifetime studying spells to gain power. Player: power
Muriel: Of course, power is the most important thing in the universe. Player: wisdom
Muriel: The wisdom of spellcasting is the source of power. Player: king or Tibianus
Muriel: The king is a patron of the arcane arts. Player: name
Muriel: You may call me Muriel. Player: spell
Muriel: Sorry, I only sell spells to sorcerers. Player: army or general
Muriel: We supply the army with some sorcerer recruits now and then. Player: Arcian
Muriel: Arcian was a childhood friend of mine. We studied the art of sorcery together but later, our ways parted ...
Muriel: Whereas I stayed here to instruct young new sorcerers, he devoted his life to his own studies ...
Muriel: Since his experiments tended to become a bit dangerous and he wanted to further explore a magic phenomenon he discovered in the Plains of Havoc anyway, he moved there and took his wife and his two assistants with him ...
Muriel: We stayed in contact for a while and he maintained a one-way teleporter to the academy. As I was missing any message from him for some time, I travelled to the plains to learn what might have happened ...
Muriel: I found the house overrun by ghouls, and no living soul. I have to assume that those ghouls have killed them and dragged everyone in their lairs. I left as soon as I could ...
Muriel: I wouldn't have wanted to see what they've done to my old friend. It's a sad story indeed. Player: Porgol
Muriel: Porgol was a quite bright student, although a bit overambitious. I was surprised when he agreed to accompany my friend Arcian to the Plains of Havoc to support him in his studies ...
Muriel: I was quite sure he'd rather study at the Edron academy instead. But sometimes people surprise one in a positive way. All the more it is tragic he found his death in this assault of undead on Arcian's house. Player: Laira
Muriel: Laira was the wife of my childhood friend Arcian. She was a warm and caring person. I hope she had not to suffer for long as ... she was killed by the undead. Sorry, I don't want to speak about that matter anymore. Player: ancestors
Muriel: There have been many generations of sorcerers in the past. Today, a lot of people want to join us. Player: news
Muriel: Our guild is working on a new spell, but I won't give away any details yet. Player: mission
Muriel: Indeed there is something to be done, but I need someone more experienced. Come back later if you want to. Player: time
Muriel: Time is unimportant.
Muriel: He's not a jester but a poor joke himself. Player: Baxter
Muriel: I don't know him. Player: Eclesius
Muriel: I don't think he's any competition. I rarely see him anyway and I don't deem his skills noteworthy. Player: Elane
Muriel: She is quite proud of her puny magic tricks. Player: Frodo
Muriel: A bar is no place that suits a scholar like me. Player: Gregor
Muriel: Knights! Childs with swords. Not worth of any attention. Player: Harkath Bloodblade
Muriel: He's not as dumb as the average fighter but a warrior nonetheless. Player: Lugri
Muriel: He is rumoured to possess some secrets our guild might find ... interesting. Player: Lungelen
Muriel: She keeps the whole wisdom of our ancestors and leads our guild. Player: Lynda
Muriel: Pretty and compentent. Player: Marvic
Muriel: Marvik and his sorcerers lack spells with real power. Player: McRonald
Muriel: Simple farmers. Player: Muriel
Muriel: I don't like jokes about my name! Player: Oswald
Muriel: Only his boss keeps him from being burnt to ashes. Player: Quentin
Muriel: He has some minor magic powers. Player: Sam
Muriel: A simple smith. Player: Xodet
Muriel: He has our permission to sell mana fluids.