If bathtub replace you have a cracked windshield replace it don't settle for windshield repair. It is bogus. If your insurance company insists on windshield repair, refuse that type of service and demand a new one. You have that right and you also have the right to choose your own glass company.
Examine the washer and replace it with a new one. Also replace screws in water line repair case they are old and damaged too. The new ones you buy should be durable and of good quality.
One other common design that is considered "washerless" was made famous by Delta and copied by several other makers. It uses little "cup" seals that fit over springs recessed in the back of the valve body. The springs press these "seals" against the cartridge and regulate the flow through little tapered openings in the cartridge. If you have one of these and it's dripping, changing these springs and seals will usually correct it. Here's a tip. Once you have the cartridge out of the way, insert a phillips screwdriver into the seal and pop both the seal and spring out. Stick the new ones on the end of the screwdriver to help guide them into place. This is especially helpful if you don't have long slender fingers.
A plumber becomes a journeyman once they complete their apprenticeship program and they can apply to be licensed. Most of the plumbers today are in the field of journeyman. To get a license to be a journeyman, you need to pass an exam and pay a licensing fee.
Remove the cap of the faucet using slip-joint pliers. Tape the teeth of the pliers to prevent damage of the surface. Remove the faucet cam washer and water line repair the rotating ball.
Keep your hands clean and dry. Plumbing jobs get slippery, so it's important to work with a pair of sturdy gloves so you don't lose your grip and accidentally hurt yourself or break something.
Over the counter drain cleaning products offer convenience and effective results. However, they are best left to those who need to simply improve the flow of water, not those who need to repair it.