Characters are meant to grow as the game progresses. Sometimes, a character will overcome one of their flaws during the course of the adventure. You might even take a feat that conflicts with or cancels out the effects of your flaws. When this occurs, the conflicting flaw is removed from your character sheet, and you must pay the difference from your Character Points Available (CPA.) This is known as a Flaw Buyback.
Flaw Buybacks can cause your CPA value to drop to a negative number. If this occurs, you won't be able to take any more feats until you've earned enough character points to "pay off" the negative balance.
Flaw buybacks do not subtract from your Character Point Total (CPT.)
Sometimes, a class offers a special feature that is effectively an improved version of a general feat or skill feat. If the feature lists the feat it improves on as a Sellback, you can remove the redundant feat from your character sheet and return the character points spent on it to your CPA.