They will quote an hourly rate for their time and tell the customer that they work on a time and materials basis. That means X many dollars per hour of time, plus the cost of parts and supplies. Most shops also charge for research time, shipping of parts, recycling, rags and so forth.
You must be 18 years old to get a credit card by yourself. While you can legally get a credit card as young as age 18, the law requires you have your own steady source of income to qualify for a credit card. Unfortunately, a monthly allowance from your parents doesn't count. It's for your own good.
Thank you for posting on the forum. Valid credit card information is needed to prove that you are an adult if your child is 12 years old or younger. No charges are made to your credit card, and your credit card number is not saved. The information is used only to validate that you are of legal age. The legal adult age varies by country and region.