what exactly is tech brockering and how is it different from tech trading?
In civ4 there was a custom game option called "No Tech Brokering", separate from "No Tech Trading". It was kind of in between Tech Trading and No Tech Trading, in that you could offer for trade techs that you researched yourself, but you could not put on the table any techs that you acquired through trade deals. This was the same for other civs of course.
The main attraction of the option was preventing AIs from selling your tech to all their friends one turn after you trade it to them. In BtS, it got a bit complicated with espionage... IIRC you could trade away techs that you stole from other civs.
A nickname for the option could be "No second-hand tech selling".