The normal is that they send you more than what you agreed to and then they ask for the extra to be sent back. Then before the full transaction takes place it turns out the money they were sending you was bogus so your bank deletes it from your account but by then your personal money has been sent from your bank back to the couple. This is a scam for sure.

If you do go through with it do not under any circumstances have further dealings with them until they actually get here - ie if they are due a refund tell them they will get it when they get here.