You go to a mechanic to investigate a weird rattling sound, and suddenly the repair costs are stacking up for problems and replacement parts you never knew existed. Do you trust the knowledge and experience of the mechanic or do you investigate for yourself?

A little legwork can go a long way towards saving money on auto repairs. John Hutchinson of Red Rocket Auto Tech explains how mechanics are taking their customers for a ride using a technique called 'dirty parts'. Dirty parts are parts that come from your car covered in grime and oil from use. A mechanic shows the dirty part to a customer as if there is something wrong with it, when really the part is perfectly good, if only suffering from a cosmetic problem.

When it comes to auto repairs you can save yourself some money, and grief, by being pro active and educating yourself. Follow these steps:

Ask Questions. Ask what tests were performed on the part, what the parts limits were, and why the part is not in good working order. If the mechanic can show you exactly what is wrong with it, rather than just the over all appearance you may be on the up and up. Ask how imperative it is to get the part replace and how your driving will be affected if it goes out, they may be making a mountain out of a molehill.

See The New Part. If the part needs to be replaced and you're satisfied with the explanations from your mechanic ask to see the new part being put into the car. Sometimes shops will charge customers for new parts while using refurbished or junkyard parts in the actual repair. You want to see the part in its original packaging before it goes into your vehicle. Anything marked Original Equipment Manufacturer or OEM is preferable, as your brand's company distributes these parts for use in your car.

Shop Around For Repair Costs. A recent study from the Northwestern Kellogg School of Management and AutoMD found that when a customer displayed knowledge of how much a repair should cost they were consistently quoted lower amounts. By calling other local repair shops and getting multiple estimates you could be able to get a lower price from your own mechanic.