It doesn't matter where you buy from. No shop is going to QT every coral coming in the door. Imagine trying to maintain a system like SC does, and still add a truckload of new corals to it every week, or two. I don't know how they keep things as in check as they do.
I can say I have bought a lot of livestock through SC, and I have also been to more than a few frag swaps. I've found pests/parasites from locals after swaps almost every time. To the best of my knowledge I've never gotten any from SC. It's just a good idea to QT/dip/inspect everything.