Why is this a competition? What's the rush? The transaction isn't done until the buyer receives his product, is satisfied and all chance of dispute are past. Only then, buying or selling, do I leave feedback. As a seller I'm not going to leave feedback the moment the money arrives, only to have the buyer make accusations against me to get out of buyer's remorse.
It's also not a standoff. "He didn't leave me feedback, therefore I won't leave him feedback." That's not honest. Feedback isn't cash. If they followed through with their end, I'll leave good feedback regardless. You can't know why someone didn't leave feedback first. Maybe he's waiting for you first. It just strikes me as kind of petty.