I want to order a MacBook Pro with trade-in service

They will not give you the trade-in value until they have verified the device. So, yes, as FoxFifth explained, you'll get billed the whole amount but will get a credit back once they have seen your device and made sure that it's in the condition you represent it to be.

When I purchased online in the U.S., they billed my credit card for the full amount of the purchase and then when they received my trade they credited my credit card for the trade amount. In my case, the trade-in credit was applied to my credit card account before the payment for the purchase was due.