B/S/T etiquette question

[pokerplyr80]

Not too long ago I saw a member post on a listing he was upset another member sold a card before he had enough time to respond to a counter offer, and seemed to believe the seller should have waited for his response. I recently found myself in a similar situation, having sent a counter offer, received no response, and then received a different offer that I accepted. I quickly updated my post that the item was sold and messaged the member and let him know. He did respond and said thanks for letting him know and that was the end of it.

My thought is that if there is no commitment to buy the card is fair game and a seller should be free to sell to anyone. But if you send a counter offer should you wait any certain amount of time for a response before selling to someone else? I am by no means asking if this should be a rule, just curious what other members think.