I think there should be a way to allow pre-sale comments.
That would also work in reverse then, right, where the potential seller could leave feedback on you? Such as:
"Avoid this tire-kicking seller like the plague. I don't know who this guy is but he popped up out of nowhere and his first question was if there was a guarantee on used merchandise. What a laugh! Don't let him waste your time."
To be clear, as a buyer, I understand your disappointment. It's happened to me here. But I prefer to see a seller's non-response as just a good reason to avoid that seller. So I move on.