Here in the western U.S. (welcome back, by the way, long time) we can see, however rarely, two distinct groups of people that you describe.
Both tend to appear immediately following any natural disaster, such as tornados, floods or other catastrophes especially those during which homes are damaged or destroyed.
Of the two groups, the 'Romanis' and the 'Travellers', the ones least seen are the Romanis; a distinct cultural and racial group apparently descended from peoples of India or even Pakistan (before it was Pakistan) as early as the 1100'sAD. They are apparently few in number but are still very clan like in their existence.
The Travellers, however are a different story. They are descended from Scots-Irish who immigrated to this country very early on... perhaps the 1600's and settled in the South-east U.S., primarily in areas that later became the Carolinas (North and South). (I'm of Scottish descent, lest anyone launch accusations of racial profiling). The Travellers live in fenced and gated compounds in very expensive homes and drive very expensive vehicles. They were, originally, horse and mule traders.
Adhering to the Clan construct of ancient Scotland and Ireland, they (along with Romanis and others seeking opportunity in the disaster's effects) show up regularly to "repair" damaged roofs and structures for a seemingly inexpensive cost, only for the homeowner to discover a "fake" repair. Little, if any follow-up prosecution occurs because they simply disappear.
Numerous news articles, both print and electronic have been produced about the Travellers but not to much effect. In the interest of full disclosure, I have never had any dealings with either group so all of the above can only be classified as anecdotal...