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.
Credit & Debt Management. People with no credit often have the most difficult time getting approved for a credit card. That's because most credit card issuers require a credit score to approve a new credit card application. However, you won't have a credit score until you have at least one active account on your credit report for six months. Some credit card issuers realize that people have trouble getting a credit card for the first time and they've made credit cards specifically for people with no credit.