Anya tells Willow she is only learning how to drive, yet in season 3's Graduation Day: Part 1 (1999) she tells Xander she has a car outside to flee in and invites him along, saying they can take turns driving.
At 34:14, Olaf comes stomping into the Magic Box carrying his hammer, but when the view cuts from his feet (and hammer) to a waist-up shot, his hands are suddenly empty. Then, after he picks up Willow and Anya and tosses them over the counter, suddenly his hammer is back in his hand again. It disappears a second time after he conks Xander with it, then reappears when Buffy arrives.
Buffy folds her class syllabus in half then after a cut folds it again.
According to Selfless (2002) in her mortal life Anya had been known as Aud, not Anyanka, and this would therefore be the name that Olaf would know her by, not Anyanka as he calls her multiple times. Since we hear him speaking English (which he could not have known), we are probably hearing him in translation, with "Anyanka" spoken for the viewers' benefit.
Strings can be seen when Willow is using magic to lift some objects at the Magic Box.
Obvious stunt double when Olaf throws Buffy across the room.