Not only do plumber apprentices have to complete their training and education to receive their licenses, they also are required to pass a criminal background check and carry liability insurance. Hiring just anybody can make you vulnerable to fraud since unlicensed plumbers might not know what they're doing or could pretend to fix something and end up charging you for the incomplete work.
Sometimes a faucet leak can be stopped by replacing the rubber washer at the end of a faucet stem or cartridge. This is a more common repair on older fixtures when things were built to last and designed to be able to be maintained. Other times the whole stem or cartridge needs replacement or the bibb seat deeper back into the fixture needs replacement. That leads to matching up the right components and often times making a trip to the hardware store or plumbing supply house necessary due to the many varieties, makes and models of faucets. My advice is to make sure your Plumber has faucet repair kit on their truck before having them come out to assess the issue.