They started as “tinkers” after the Famine in Ireland and got the name from fixing pots and pans etc. I saw them in Ireland a few years ago and the tour guide said the richest antique dealers in Ireland today were travelers. They have carvan camps in some areas of the brithish isles for them to stay. There was a National Geographic article on them a while back. I read about them in a cultural anthropology book for the class and it was quite interesting. You might start looking for info in those sources.
people keep mentioning the 60 minutes story from about 5 years ago. Does anyone know where I can find the video?