Reminder: The seller only used the word "asking" and the seller never used the term "asking price." Keith used the term "asking price."
But, as a basis for discussion, let's say the seller used the term BIN ("Buy It Now") and offered Keith a BIN of $10,000.
The seller would still not be obligated to sell, as explained by
@Mod Team Echo, because Keith countered that offer. If you counter an offer to sell, then that is a rejection to the offer and it becomes null and void, even if you change your mind minutes later and want to accept it. Then, your offer to pay $10,000 after rejecting it becomes a new $10,000 offer that the seller must accept before it becomes an agreement.
These are the standards we use for negotiations as moderators.