In 14 CFR Part 1.1 Definitions and Abbreviations - you will find a definintion for Commercial Operator:

"...means a person who, for compensation or hire, engages in the carriage by aircraft in air commerce of persons or property other than as an air carrier...Where it is doubtful that an operation is for compensation or hire, the test applied is whether the carriage by air is merely incidental to the person's other business or is, in itself, a major enterprise for profit."

The FAA is VERY LIBERAL in interperting this statement. The scenario presented would be "for compensation and hire" because the flight is not incidental to the commercial pilot, but for the pure benefit of the passenger. As someone else said in the thread, opportunity for free flight time has been interperted in the past by the FAA as compensation to an aspiring commercial pilot.

That said what can a basic 250 hr commercial pilot do? That's found in 14 CFR Part 119.1 (e) - it contains a list of activities including student instruction, ferry (aircraft only, not pax) or training flights, banner towing, crop dusting, etc. - 119.1 (e) (1) - 119.1 (e) (10). Anything else most likely, but not necessarily, will fall under Part 121, 135, or 125. This is why the FAA has a fairly easy process (for the FAA) under Part 135 to obtain a "single pilot" 135 certificate to allow carriage of passengers, and it does require the PIC have more time than the basic 250 hours.

Your CFI should be able to go over this in detail with you.

There are AC's on this...I will look for them in a moment.