I've had success for decades (1982 to present) as a result of a good working relationship with the parts guy at a local dealership. Typical discount was 20% off his retail. When I moved 30 miles further away, he'd even ship me stuff for free. The big plus there was that I always got the right parts because he knew his vehicles.
Then there's the tips and advice. One example - in 2012, we were planning a family vacation to the Rockies that would run 6000-7000 miles. My 2001 had about 170k miles on it, and he asked if I'd ever replaced the radiator. I said no, and he explained the risk of having the pink milkshake in the middle of nowhere. I'd never even heard of that (now typical) 3rd Gen problem. So I bought the radiator from him and replaced it, and happily never got to experience that failure.
So for me personally, the local relationship trumps a lot of things, and is even worth paying a little more to get the benefits. If I were you, I'd go to a dealership and talk face to face with the parts guy. Ask him if he's willing to give discounts to faithful customers. If he does, and they're decent discounts, reward him with your business. If not, you lost nothing.