There are instances where the amount on a pending charge changes when a charge is actually posted. For example, when you leave a tip at the restaurant, your pending charge shows the pre-tip amount, and when it posts, the charge is for the full bill, with tip included.
Let's say I called my credit card company and told them to stop further payments to a merchant that currently has a transaction pending for $50. Although they can no longer make another charge to my account, will they be able to increase the amount of that charge when it posts? Is there any way to ensure that $50 is the maximum they take out for that charge?