It may just be stressed from the shipping. Set it up in an appropriate enclosure away from your regular collection...observe all quarantine practices...and just let it be. Check again in a week and see if you still see any signs of potential RI.

In the meantime, definitely let the breeder know of your concerns as quickly as possible. Tell him of your plans to let the snake settle in and have a chance to recover from the stress and then you'll make a more thorough check of his breathing. And ask the breeder if he believes you should do anything differently than I've suggested. He may know something about the snake that we don't...or he may have some specific procedure you must follow (ie: getting the snake to a vet asap) in order to fulfill his warranty conditions.