Mechanic charges woman $3400 for an oil change that should've only cost $120: 'They required windshield wipers and parking lights be replaced.'

The mechanic was celebrating the second she walked out of the garage. 

One of the best ways to avoid getting scammed is knowing what things should cost. A bodega clerk once tried to charge me $12 for a pack of Hostess cupcakes and a 20-oz bottle of Diet Coke, and I immediately called him out. It was either an honest mistake or he looked at me and thought he could get away with charging an exorbitant amount for what the product was worth, because I wouldn't be paying attention. In that instance, I had a feeling it was the latter, and it wasn't the first time it happened. 

If you walk into a car dealership telling the car salesman, "I don't know anything about selling a car," he's going to make sure that you walk out of there with the most expensive car, with the highest interest rate, and with the least amount of money down as possible. He knows how to squeeze every penny out of you in the long run in a way that will feel like a "good deal" to an ignorant person. 

Knowing the average price of a product when making a purchase (and while playing The Price is Right) is the bare minimum when entering a customer service situation. If you don't have that, you should rely on your intuition. If you have a feeling that you're getting scammed, there's a good chance you are. The woman in this story didn't stop to ask her husband if spending $3400 on an oil change was a good price, and it cost them both just that: $3400.