I've learned that good intentions are filtered differently when the other party is already angry.
If my customer is having a problem, I can try being friendly after the communication is already ongoing, problem has been aknowledged, and it is on his way to be fixed. Ending in a friendly tone is a big plus. Starting with it, not at all.
On the other hand, as a customer, having to deal with you at all is already stressful enough, i'm paying you and still losing time over your screw-ups, and still you start with an "ooof". It would give me a feeling of "not only i'm losing time, i'm also being joked on".
Being professional and gradually friendly is simply the most secure way to operate, because every person that contacts you for a problem, big or small, doesn't want to contact you to begin with. Don't "ooof" me please.