When you make an offer using credit card, we "authorize" that amount, which result in a "Pending" status. Think of "Pending" as a hold, but not yet formally placed on your card as a charge. (Some credit card statements don't even show transactions that are "pending.")
If the seller doesn't accept the offer, or if the offer is expired, or if you decides to cancel the offer before it is accepted, the transaction is voided. Depends on your credit card processor, the "pending" transaction will drop off after couple business days.
On another note, if the seller accepted your offer, the charge will converted from pending to settled. But do not worry, the money is placed in escrow until you press "complete" (to release it from escrow).
if you see the item in person and don't like it, or (seller decides not to sell anymore), just can just cancel (instead of pressing "complete") and we'll refund the transaction if the original transaction is settled.