Additionally, the way you worded this: "Asking best offer takes it. This ad will be up until midnight 11/15 eastern time." literally means "If 5 people make me offers (for example) of $5, $10, $15, $20, and $25, I will sell to the highest bidder."
Yes, I spent many years teaching English, but I'm not an attorney, so I do not know if my interpretation of your English would be legally binding. I'm not trying to be a smart ass BTW. I am trying to be helpful.