Alison MacG Dec 2, 2015:

Agree with Neil I think that here "saw a good thing" = "knew a good thing when they saw it".
Other examples of this usage:
He married because he wanted a meal ticket. He wanted an easy mark to pay his bar bills and a substantial trunk to drop his glad rags in. He saw a good thing and he played it for all it was worth.
http://www.forgottenbooks.com/readbook_text/Uncle_Charlies_S...
Arny was certainly not a dummy. He knew a good thing when he saw it. And right now, Harry was a good thing. A steady meal ticket.
https://books.google.co.uk/books?id=_Ya7DhoQSSAC&pg=PT73&lpg...

Neil Ashby Dec 2, 2015:

"Some relatives saw a good thing and I think [THEY] maybe saw an opportunity to--to cash in."

As simple as that I believe.

No need to stretch it out and add meaning that's not there: "Some relatives saw a good thing and I think [SOME OTHER RELATIVES] maybe saw an opportunity to--to cash in."

Terry, the "and" is not necessarily used to form a list of items (different groups of relatives) but rather to introduce a new clause; the narrator's opinion about the "relatives who saw a good thing". Clearly the "good thing" is an opportunity to cash-in.
Secondly why do think I'm answering with the question itself? My suggestion is "a winning ticket" - as in "cash-in a winning ticket". And the second part of my answer is "yes" in response to KLP's question "Does it mean the same as 'an opportunity to cash in'?"

John Detre Dec 2, 2015:

Logically and grammatically, Terry is quite right, a distinction is being made between “saw a good thing” and the “opportunity to cash in” (which is apparently less definite than the “good thing”), so they must be two different things. However, it seems to me that "saw a good thing" connotes self-interest more than disinterested enthusiasm, so perhaps the distinction being made is between a non-monetary gain (a “good thing” in the sense of reflected glory for themselves or some other benefit) and the possibility of making money on the deal to boot?