When you get your commercial certificate you may be paid for your piloting services. However, Part 61 is somewhat vague on the details, especially the part referring to restrictions in other parts of the FARs.
(a) Privileges—(1) General. A person who holds a commercial pilot certificate may act as pilot in command of an aircraft—
(i) Carrying persons or property for compensation or hire, provided the person is qualified in accordance with this part and with the applicable parts of this chapter that apply to the operation; and
(ii) For compensation or hire, provided the person is qualified in accordance with this part and with the applicable parts of this chapter that apply to the operation.
There may be other restrictions dependent on the type of operation that is being conducted but in general you may fly for:
A company engaged in common carriage—you will carry persons or property for hire for the general public. Airlines and package delivery companies like FedEx and UPS fall into this category and they offer Scheduled Air Service or Chartered Large Aircraft. Part 121 governs passenger carrying operations and Part 119 governs package delivery companies. On-Demand Air Service where the customers generally charter the whole airplane at a time and destination that they choose fall under Part 135—commonly referred to as Charter Operators.
A company not involved in common carriage that operate large aircraft to carry their own goods or people or goods for a small number of customers (typically less than 4) Part 125 governs their activities.
Corporate Flight Departments operating smaller aircraft fall under Part 91. Part 91 operations also include flights that are incidental to the business of the company, e.g. aerial views of real estate or transporting customers to remote destinations in the course of business.
A commercial certificate is required to be paid in any of these operations. However, an ATP may be required depending on the aircraft and operation.
Part 119 list somethings that do not fall under the rules for Part 121, 125, and 135. These include things like:
• Nonstop Commercial Air Tours conducted within a 25-statute mile radius of that airport, in compliance with the Letter of Authorization issued under §91.147
• Ferry or training flights
• Crop dusting, seeding, spraying, and bird chasing
• Banner towing
• Aerial photography or survey
• Nonstop flights conducted within a 25-statute-mile radius of the airport of takeoff carrying persons or objects for the purpose of conducting intentional parachute operations
• Small UAS operations conducted under part 107 of this chapter
You can use your commercial certificate to transport persons or property for hire but the FAA doesn’t want you to be acting like a Part 121 or Part 135 carrier. The way they determine if you have been acting that way is whether you have been “holding out” your services. AC 120-12A Private Carriage Versus Common Carriage of Persons or Property defines it as:
A carrier is holding out when they represent themselves as willing to furnish transportation within the limits of its facilities to any person who wants it.
There are four elements in defining a common carrier: (1) a holding out of a willingness to (2) transport persons or property (3) from place to place (4) for compensation. This holding out which makes a person a common carrier can be done in many ways and it does not matter how it is done.
c. Physically holding out without advertising where a reputation to server all is gained is sufficient to constitute and offer to carry all customers.
If you are a newly minted commercial pilot with your instrument rating and you want to build hours toward your ATP or just make some money, you can’t put an ad on Craigslist advertising that you are willing to fly anyone anywhere. You can mention to your fight school that you would be willing to fly people in their airplanes. If you get a customer who travels to one of their remote locations in their airplane every week and they want you to fly them, then that’s OK. If they mention to their friends how much more relaxed they feel when they arrive and you start flying them in their airplanes too, that’s OK too.
You can even use your airplane to fly them, but you have to comply with the 100-hour inspections, upgrade your insurance policy for commercial operations, and comply with Part 135 or Part 119 non-common carrier operations rules. You need a operating certificate for that.