As soon as I finished researching Stock Exchange, the Drengin ambassador comes to me with an offer.
"We are not proud to admit it, but our scientists have yet to make a breakthrough in that dept."
He offers me Advanced Trade in exchange for Stock Exchange, and I accept.

But Advanced Trade pops right back up into his list of things he can sell me, even though Stock Exchange disappeared from mine. Perhaps his courier went "missing"?

It's an interesting political maneuver, and quite appropriate for the Drengin to pull a fast one. But it doesn't seem that I have such ability or the consequences that go with it.