No person why certificate may holds a private pilot act as a pilot-in-command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as PIC of an aircraft.
A private pilot...
a. may act as PIC of an aircraft in connection with any business or employment if it is only incidental to that business or employment and does not carry passengers or property for compensation or hire.
b. may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.
c. may act as PIC of a charitable, nonprofit, or community event flight described in 14 CFR 91.146, if the sponsor and pilot comply with the requirements of that regulation.
d. may be reimbursed for aircraft operating expenses that are directly related to search and location operations provided the expenses involve only fuel, oil, airport expenditures, or rental fees, and the operation is sanctioned and under the direction and control of local, state, or federal agencies or organizations that search and location operations.
e. may demonstrate an aircraft in flight to a prospective buyer if the private pilot is an aircraft salesman and has at least 200 hours of logged flight time.
f. may act as PIC of an aircraft towing a glider or unpowered ultralight vehicle, provided they meet the requirements of 14 CFR 61.69.
g. may act as PIC for the purpose of conduction a production flight test in a light-sport aircraft intended for certification in the light-sport category, provided they meet the requirements of 14 CFR 61.113(h).