i would like to ask about the online purchasing..

1) what if they charge different amount that we purchase.
2) for the hotel right, i would like to make the room on the status of confirm through online and paid the balance by cash on that day. cause the hotel will hold some amount for the credit card.
and i not sure hows it works for debit card? would they deduct certain amount of the account and then paid it back to the account... coz the whole transaction i would be paid by cash instead of debit card.. the reason using debit it just for confirm of the room.