I read this novel about 15 years ago, but I only remember one scene from it. I believe the setting was similar to that of the Bartimaeus Sequence: an alternate modern-day world where magic is common, although not everyone can use it.
The protagonist (who was either a novice magic-user or maybe couldn't use magic at all) got into some kind of dispute with a powerful wizard and ended up having to go to court over it. On the day of the trial the wizard doesn't show up, so the protagonist just explains their side of the story. They give a simple, truthful account of what happened. But just as the judge is about to side with the protagonist, the wizard suddenly bursts into the courtroom and gives a flagrantly embellished version of the events that paints the protagonist in a bad light. Of course the judge/jury immediately change their mind and side with the wizard instead.
The protagonist has to pay damages to the wizard, and is relieved to find out that the amount they have to pay is not too much. But there's a nasty surprise: it's tradition that any courtroom fees incurred by the winner are transferred to the loser. Since the wizard was late to the trial, the protagonist now owed a hefty late fee that was several times the amount of the damages!
Any ideas what this scene is from?