If you sell knives in Germany, or Argentina, they will probably say Vacht-mann. Other places, they may mis-pronounce it as Watch-man, but they still will have it right on the knife. Once people know who you are, they will learn how it is pronounced.
IIRC, Wachtman is a Jewish surname. I had a friend named Wachtsman, and he said it used to be Wachtman before his family emigrated to the US. He has so much trouble as a businessman with people switching the letters he changed it to Waitsman.
I would like to know where you live, and where your family came from. BTW, fill out your profile, so your location and some info about you will be available.