I disagree with Stawka: just because it doesn't affect your seller rating doesn't mean that you shouldn't follow it up. I mean, if item not received and item not as described complaints didn't affect my rating, I'd still follow them up, because I want to provide good service. I would follow up neutral or negative feedback for the same reason - if a buyer isn't happy with their item then it helps me to know why, and I dont think there's anything wrong with sending one (non-accusatory) message in an attempt to find out/solve the problem. However, if they respond defensively or aggressively, leave them alone. You're only going to make it worse.