In the past, a good portion of auto shops have overcharged their customers on parts. They realized they good give a small discount on dealer list for parts while actually selling the cheapest part they could find. Some mechanics were seeing profits from auto parts in the 200-300% range. Car owners have since wised up. With a lot of auto parts wholesalers starting their own websites to sell to the general public, consumers have realized they can actually buy the parts themselves at considerably discounted prices. On average, a person can save anywhere from 40-60% off what the mechanic would charge. The best advantage to this is they are getting much higher quality parts at half the cost. Sites such as Autohaus Arizona offer high quality parts at heavily discounted pricing.
While some mechanics are fighting this change, quite a few are embracing it. They realize they no longer are responsible for warranties on parts. Also, they no longer have to worry about paying their parts suppliers on time. In fact, some mechanics actually give out web addresses to companies they want their customers to purchase from. Even though they lose the profit they would have made on the parts, they will generally have fewer headaches when it comes to getting such parts for their customers. A few mechanics have even gone as far as just charging more for the labor.
If you do plan on buying your own parts to bring to the mechanic, make sure you check with your mechanic. Some mechanics still do not allow people to bring their own parts. You do not have to be stuck with having to return parts because your mechanic has decided he wants to overcharge you for lower quality parts.