Who do most use for buying parts, dealer or other.
I need At this point a set of heated mirrors (I think) and although not cheap as you get what you pay for but also don't want to pay 20% more for something that is the same as the one for 80%.
Best prices I've seen on legitimate parts is from 1stvwparts.com. It's a DBA or storefront for the Auburn Volkswagen dealership service department in WA, and their stuff is real. The only downside is you may wait a little while depending on what you need and where you're at. They usually needed 2 business days to get my order in, and another 3 to 5 business days to get it from WA to OH.
I've also done a lot of business with ECS Tuning. Their prices aren't quite as good, on average, but still pretty decent. They tend to have more stuff in stock, at least the common stuff, and a very good selection of aftermarket as well. If you need genuine VW/Audi parts, and they flag it as a genuine part, it's legitimate. Main benefit for me is they're in-state with me here in Ohio, so if it's in stock, I generally have it in-hand in one business day. Obviously that may not apply for you.
For salvage stuff, I used to do business with 800-VW-PARTS and could speak highly of them, but I think they've gone out of business since I last talked to them. I don't think they recovered from Hurricane Sandy. I'm not sure if the current proprietor at that number has any relationship to the old guys.
If you need a lot of parts, on an ongoing basis, don't be afraid to talk to your local dealer about a discount. The worst they can do is say no. For better or worse, I'm on a first name basis with a number of people at my dealer. I showed the parts manager a report of what I've spent in parts/service over the years (which had just tipped over into five significant digits at the time) and I got a standing flat 15% off on all my orders going forward. Not the greatest, but beats the hell out of paying full list, and sometimes that flat 15 works for me on parts the other places don't discount deeply. They also take electronic orders from me straight out of . So nothing really beats the dealer for me in terms of speed and convenience, but I still pay a bit extra for it.
Volkswagen dealers will also have access to a new line of 'economy' parts, commonly needed maintenance stuff for older vehicles. You'll see them in their catalog listed similarly to -X rebuilt parts. Supposedly good stuff made to the same standards as original. I've seen economy parts available for brake rotors and an alternator for my old 04 Passat.
Jason