If you are a do-it-yourselfer buying your own parts is the only way to go. You just have to find a mechanic who will put on your parts when you choose not to tackle the job. They are out there, you just have to find them. In my experience they tend to be good and they tend to be honest (they usually don't have high overhead, the great ethical compromiser). Any mechanic who gives you the egg/restaurant story or the steak/restaurant story - just walk out. Anyone who is that interested in the sale of the part is overcharging for the part - it's really that simple. The whole "part quality" argument is silly as well. I've been doing this for 10 years, at least $25k in parts and I've never had a replacement part fail. It is incumbent on you to buy quality parts, and to get all the parts - washers, seals, nuts - everything that is needed for the job. Where I buy parts they are all name brand, original supplier parts - Bosch, Behr, Bilstein, etc. That they don't come in a Mercedes box is of no relevance. Anyone who tells you different than this is either A) a mechanic, or B) not a do-it-yourselfer. Now if you've in a small town and you can't find the right guy, all bets are off.