If you use a promotional offer, like $50 off ~$100 off, after you have used an offer, can you just cancel it so you do not have to pay anything, or does it charge you, and you cannot cancel it unless you have paid some amount to them?
These are credits and each channel is a little different. Yahoo is Prepay, Google will can off of postpay billing where they bill each 30 days but you have to work through the billing threshold program. They have an initial threshold of $50 or 30 days then it moves to $200 or 30 days then $500 it will depend on payment history to move up the threshold Adcenter is postpay each 30 days. I don't remember if there is a progression you have to go through or not.