Agreed, bowing is a must, ignore any advice you may have heard saying not to attempt it because you would do it wrong as a gaijin.
A nod of the head here is not the same there, focus on your shoulders not your stomach and you'll do just fine. Return what you are given is what I used as rule of thumb. I got use to bowing after any transaction.
Took me a week to stop doing it once I got home
