It's hard to know.
However, none of the major airlines are charters. JetBlue and SW are not.
Basically charters tend to run fairly limited schedules and are generally not sold via a lot of normal outlets (expedia, travelocity etc.) Some of the Orlando area charters actually fly into Sanford.
Also, if you buy a some vacation packages I think you play by their rules even if you fly on a scheduled carrier. My mom, got hit up on a package she bought to Spain and she was flying United so.... that may be another area where folks are getting hit.