They were looking for new ways to become rich. Weren't they ?
(I see nothing unusual about this strucure.)

It is correct for me if the grammar structure vision. (I have no idea what you mean.) But  I don't see senteces like that very often even in a written English.

The only tag I've seen normal people using is "isn't". I a spoken sentence like:

This is a good job, isn't ?

You are looking for trouble, isn't ? (incorrect, but I heard a Canadian saying It)
(Tag questions are commonly used with I, you, he, she, we, and they.  Tags are not limited to "isn't.)
(I have not been around Canadians for years, but I find it difficult to believe they would say such a thing.  It sounds more to me like a mistake made by the native speaker of a language other than English.) 

So the question is: How Often Do You Use Question Tags ?
(Personally, I rarely use them in English.  I certainly use "né?" and "certo?" much more often in Portuguese than I use tags in English.)